2. Lago

Lago is an open source billing platform built as a direct Stripe Billing alternative for SaaS companies that need transparent, auditable invoicing combined with usage-based pricing. 

Unlike Stripe Billing, which bundles billing logic tightly with payment processing, Lago operates as a standalone billing engine. It handles subscription management, metered usage billing, invoice generation, and credit notes independently, and then delegates payment collection to whichever gateway you choose, Stripe, GoCardless, Adyen, or others.

This separation is what makes it a credible open source Stripe alternative rather than just a lightweight wrapper.

Lago is self-hostable and fully open source under the AGPL license, with a managed cloud version available for teams that prefer hosted infrastructure.

Key Features

• Subscription & usage-based billing engine: supports flat fee, per-seat, metered, graduated, package, and percentage-based pricing models, configurable without custom development

• Real-time usage metering: ingest usage events via API and aggregate them in real time for mid-cycle reporting and accurate invoice generation

• Credit wallets and prepaid credits: first-class wallet system for managing prepaid balances, promotional credits, and subscription-included allowances

• Invoicing with full audit trail: generates detailed line-item invoices that are tightly linked to underlying usage events and subscription changes, with credit note and adjustment support

• Coupons and discounts: native coupon engine supporting percentage and fixed-amount discounts, trial periods, and one-off promotions

• Multi-currency support: bill customers in their local currency across global markets without additional plugins

• Tax management: configurable tax rates per customer, region, or product, with invoice-level tax breakdowns

• Self-hostable or managed cloud: deploy on your own infrastructure for full data control, or use Lago's hosted cloud tier

Pros

• Genuinely open source with an active GitHub community and strong contributor base

• Clean separation between billing logic and payment processing no payment gateway lock-in

• Strong invoicing fidelity, well-suited for B2B SaaS with audit and compliance requirements

• No per-transaction or revenue percentage fees when self-hosted

• Supports both subscription-first and usage-first billing models

• Well-documented API with good developer experience

Cons

• AGPL license requires open-sourcing modifications if you distribute the software — some teams prefer MIT or Apache-licensed alternatives

• Usage metering is less purpose-built for extreme throughput compared to dedicated metering platforms

• Richer enterprise features (SSO, advanced RBAC, priority support) are locked to the paid cloud tier

• Less mature than legacy billing platforms for complex dunning workflows and revenue recognition

Best For

SaaS companies looking for a well-rounded open source Stripe Billing alternative with strong invoicing, subscription management, and usage-based pricing support. Particularly strong for B2B SaaS products with compliance requirements, teams that need transparent audit trails on billing events, and companies scaling past Stripe Billing's pricing constraints who want to retain payment gateway flexibility.

3. Openmeter

OpenMeter is an open source usage metering platform built for engineering teams that need to accurately measure, aggregate, and bill for product consumption at scale. 

Where most open source billing tools focus on subscription management, OpenMeter focuses specifically on the hardest part of usage-based pricing: reliably collecting, processing, and querying billions of usage events without data loss or significant latency.

OpenMeter is built in Go and runs on top of Apache Kafka and ClickHouse, giving it an architecture designed for high-throughput, event-driven workloads. 

This makes it particularly well-suited for AI companies metering token usage, API platforms tracking request volume, and infrastructure products billing for compute or storage consumption workloads where traditional billing systems fail under event volume.

As a Stripe Billing alternative, OpenMeter fits best as the metering backbone of a broader billing stack. It can integrate directly with Stripe Billing for payment collection while replacing Stripe Meter which many teams find unreliable at scale with a purpose-built, self-hosted metering layer that teams own and control.

Key features

• High-throughput event ingestion: ingest and process billions of usage events with low latency, built on Kafka for durability and ClickHouse for fast analytical queries

• Flexible aggregation: supports sum, count, unique count, and custom aggregation types on metered usage data, configurable per meter definition

• Real-time and historical queries: query current usage windows and historical consumption in real time, enabling live dashboards, limit enforcement, and accurate invoicing

• Streaming deduplication: idempotent event processing prevents double-counting usage events in distributed, retry-heavy environments

• Stripe integration: native integration allows OpenMeter to push aggregated usage data directly into Stripe Billing for invoice generation, while replacing Stripe Meter as the underlying metering layer

• REST API and SDKs: developer-first API for event ingestion and usage queries, with SDKs for major languages

• Self-hostable: deploy on your own infrastructure with full control over event data and metering logic

Pros

• Streaming deduplication is a significant reliability advantage over Stripe Meter

• Clean separation of metering from billing gives teams architectural flexibility

• Lightweight and composable fits into existing billing stacks without replacing everything

• Strong fit for AI and API-first products where metering accuracy directly impacts revenue

Cons

• Metering-only: does not handle subscriptions, invoicing, payment collection, or dunning natively  requires pairing with a billing platform

• Infrastructure complexity Kafka and ClickHouse add operational overhead compared to simpler self-hosted billing tools

• Smaller community and fewer integrations than more established billing platforms

• Not a complete Stripe Billing alternative on its own best used as a component in a broader billing architecture

Best for

Engineering teams building usage-based or consumption-based products that need a dedicated, high-reliability metering layer they fully own. Ideal for AI platforms tracking token usage, API businesses metering request volume, and infrastructure companies billing for compute especially teams who want to replace Stripe Meter with something more accurate and scalable while retaining Stripe or another gateway for payment collection.

4. Killbill

KillBill is one of the oldest and most established open source billing platforms available, with over a decade of production use across telecom companies, media platforms, and enterprise SaaS products. 

Built in Java and released under the Apache 2.0 license, KillBill is a full-featured subscription billing and payment orchestration platform designed for organizations with complex billing requirements, regulatory constraints, or legacy system integrations that modern SaaS billing tools are not built to handle.

As a Stripe Billing alternative, KillBill occupies a different position than newer platforms. It is not designed for rapid deployment or no-code configuration; it is designed for correctness, extensibility, and auditability in environments where billing errors carry significant consequences. 

Its plugin architecture allows teams to extend the core platform with custom payment gateways, tax engines, invoice renderers, and notification systems, making it highly adaptable to specialized billing environments that off-the-shelf tools cannot accommodate.

KillBill is fully self-hostable and free under Apache 2.0, though operational complexity means most production deployments require dedicated engineering investment to set up and maintain.

Key features

• Subscription lifecycle management: full support for subscription creation, trial periods, upgrades, downgrades, cancellations, pauses, and reactivations with complete event history

• Plugin architecture: extensible plugin system for custom payment gateways, fraud detection, tax calculation, invoice rendering, and notification workflows hundreds of community plugins available

• Invoice engine: generates detailed invoices with proration support, tax handling, adjustment credits, and full audit history of every billing event

• Payment orchestration: built-in payment retry logic, dunning management, and multi-gateway support including Stripe, Braintree, PayPal, Adyen, and more

• Catalog management: XML-based product catalog supporting multiple pricing plans, trial phases, add-ons, and plan version management with backward compatibility

• Analytics and reporting: built-in Kaui admin UI and analytics dashboard for subscription metrics, payment reports, and revenue reconciliation

• Multi-tenancy: native multi-tenant support for platforms and marketplaces managing billing on behalf of multiple merchants or customers

Pros

• Battle-tested in production for over a decade across complex, high-stakes billing environments

• Unmatched extensibility through plugin architecture can be adapted to virtually any billing workflow

• Apache 2.0 license no restrictions on commercial use or modification

• Strong auditing and dunning management well-suited for regulated industries

• True multi-tenancy built in, not bolted on

• Large library of community plugins for payment gateways and integrations

Cons

• Steep learning curve with Java-based, XML-configured catalog, and complex deployment requirements demand significant engineering investment

• Not designed for modern usage-based or AI billing usage metering support is limited compared to purpose-built tools

• Admin UI (Kaui) is functional but dated compared to modern billing dashboards

• Slow to iterate relative to newer platforms not ideal for teams that need to experiment with pricing quickly

• Community support has become less active compared to its peak years

Best for

Enterprise engineering teams and organizations in regulated industries, telecom, media, financial services, or large-scale B2B SaaS that need a proven, deeply extensible open source billing platform with strong auditing, multi-gateway support, and the flexibility to handle billing workflows that no off-the-shelf tool supports. 

Not the right choice for teams prioritizing fast setup, modern usage-based pricing, or no-code configuration.

5. BillaBear

BillaBear is an open source subscription billing and management platform built for SaaS businesses that need straightforward subscription management, invoicing, and tax compliance without the revenue percentage fees of Stripe Billing. 

Built in PHP using the Symfony framework and released under a permissive open source license, BillaBear is designed to be approachable for teams that do not want the operational complexity of Java-based platforms like KillBill but still want full control over their billing infrastructure.

Where more specialized open source Stripe alternatives like OpenMeter focus on metering throughput or Lago focuses on usage-based billing depth, BillaBear focuses on the operational side of billing: subscription workflows, customer lifecycle management, tax handling, and dunning automation. 

It ships with a full customer portal, PDF invoice generation, and configurable cancellation and retention flows, features that product and customer success teams rely on but often have to build separately when using Stripe Billing.

BillaBear integrates with Stripe as a payment gateway for card processing, making it a practical option for teams that want to retain Stripe's payment infrastructure while replacing Stripe Billing's subscription and invoicing layer with an open source alternative they fully control.

Key features

• Subscription management: full subscription lifecycle support including trials, plan changes, upgrades, downgrades, cancellations, and pauses with automated proration

• Customer portal: self-service portal for customers to manage their subscriptions, update payment methods, view invoices, and handle cancellations

• Tax compliance: built-in EU VAT handling, tax rate configuration by region, and tax-inclusive invoice generation for international SaaS businesses

• PDF invoice generation: automated, branded PDF invoices generated at billing events with full line-item detail and tax breakdowns

• Dunning automation: configurable dunning workflows for failed payments including retry schedules, customer notifications, and subscription suspension logic

• Cancellation and retention flows: configurable offboarding workflows to capture cancellation reasons and present retention offers before churn

• Stripe integration: integrates with Stripe for payment processing while decoupling subscription and invoicing logic from Stripe Billing

• Self-hostable: deploy on your own infrastructure with full ownership of customer and billing data

Pros

• Accessible for teams already familiar with PHP/Symfony lower barrier to self-hosting and customization than Java-based alternatives

• Strong out-of-the-box tax and VAT handling for European and international SaaS

• Customer portal and cancellation flows reduce the operational surface area teams need to build themselves

• No revenue percentage fees replace Stripe Billing's subscription layer without paying for it per dollar of MRR

• Clean integration model: use Stripe for payments, BillaBear for billing logic

Cons

• Limited support for usage-based or consumption-based billing designed primarily for seat-based and flat-rate subscriptions

• Smaller community and ecosystem than Lago or KillBill

• Less suitable for high-growth AI or API-first products where metered pricing is central to the business model

• PHP stack may not align with the technology preferences of all engineering teams

Best for

SaaS companies with simple subscription models flat-rate, per-seat, or tiered plans that want to replace Stripe Billing with an open source billing layer they own and control. 

Particularly well-suited for European SaaS businesses that need robust VAT and tax compliance out of the box, and teams that value customer-facing billing workflows like self-service portals and retention flows alongside core invoicing and subscription management.

Features to look for in an open source alternative to Stripe Billing

Not every Stripe alternative deserves your attention. Most are either closed-source SaaS tools with the same lock-in problems as Stripe, or lightweight libraries that leave you stitching together billing logic yourself. Before you evaluate any open source Stripe alternative, here's what actually matters.

• Real-time usage metering

Stripe Billing was built for subscriptions. If your product charges based on API calls, tokens, compute, or any event-driven metric, you're fighting the tool from day one. An open source alternative worth using should meter usage in real time, not batch it, not estimate it, not require you to push data manually at the end of a billing cycle.

• Flexible pricing model support

Your pricing will evolve. What starts as a flat subscription almost always moves toward usage-based, credit-based, or hybrid models as your product matures. Look for a billing platform that supports all of these natively: flat fees, per-unit, tiered, volume, credit wallets, prepaid packages, without custom workarounds for each.

• Credit and wallet infrastructure

This is the feature most billing tools skip entirely. If you sell prepaid credits, tokens, or usage packs, you need native wallet management: balance tracking, expiry, top-ups, and consumption logic. Bolting this onto Stripe means custom tables, custom logic, and a support headache every time something goes wrong.

• Self-hosting with full data ownership

The whole point of going open source is control. Your billing data (customer records, invoices, usage events) should live where you decide, not in a third-party's cloud. Look for a platform you can deploy on your own infrastructure, with no vendor holding your data hostage.

• Clean separation from your product codebase

Billing logic embedded in your application code is a long-term liability. Good billing infrastructure runs as a separate service your product talks to via API, so billing changes don't require product deploys and finance teams can experiment with pricing without involving engineering every time.

• Enterprise-ready from day one

Discounts, overrides, custom contracts, multi-currency, invoice customization. These aren't edge cases for most growing SaaS or AI companies, they're table stakes. If your billing platform can't handle them cleanly, you'll be back to custom workarounds within six months.

• Active development and community

Open source software is only as good as the team behind it. Check the GitHub commit history. Are issues being addressed? Is the roadmap public? A project with 3,000+ stars and active maintainers is a very different bet from an abandoned repo with a promising README.

Why Flexprice is the best open source alternative to Stripe billing

Flexprice was built specifically for the problem Stripe Billing doesn't solve well: usage-based and credit-driven billing for AI and SaaS companies that need flexibility, real-time accuracy, and full infrastructure control.

Here's why it stands out.

• It's built for usage-based billing, not retrofitted for it. Stripe started with subscriptions. Usage billing was added later, and it shows. Metered billing on Stripe requires aggregating usage manually, has limited real-time visibility, and gets complicated fast at scale. Flexprice was designed from the ground up around usage events. You send an event, Flexprice handles the rest: metering, aggregation, billing calculation, and invoice generation.

• Native credit and wallet system. Most billing platforms treat credits as an afterthought. Flexprice ships with a full credit wallet infrastructure: prepaid balances, credit expiry, usage deduction, top-up flows, and real-time balance visibility. If you're building an AI product where customers buy token packs or credit bundles, this alone saves weeks of custom engineering.

• Every major pricing model, out of the box. Flat rate, per-unit, tiered, volume, BPS, credit-based, prepaid. Flexprice supports them all without configuration gymnastics. You can mix and match pricing models across a single plan, which matters when your enterprise customers want something slightly different from your self-serve tier.

• Self-hosted and open source. Your billing data stays on your infrastructure. No revenue sharing, no per-transaction fees on top of what you're already paying, no SaaS vendor with access to your customer financial data. Flexprice is MIT licensed, so you can audit every line, fork it, and deploy it wherever your team is comfortable.

• Integrates with Stripe without replacing your payment flow. You don't have to rip out Stripe entirely. Flexprice handles the billing logic and metering layer while Stripe (or another payment processor) handles the actual payment collection. You keep Stripe's payment reliability while replacing the part that actually frustrated you: the pricing and metering infrastructure.

• 3,500+ GitHub stars and growing. Flexprice has earned trust from early-stage AI startups and scaling SaaS companies alike. The codebase is actively maintained, the roadmap is public, and the community is real, not manufactured.

• If you've outgrown Stripe Billing's pricing model limitations, or you're building usage-based pricing from scratch and don't want to spend six months on billing infrastructure, Flexprice is the open source alternative built for exactly where you are.

Wrapping up

Stripe Billing is a solid starting point, but it wasn't built for the way modern SaaS and AI companies price their products. As usage-based models, credit systems, and hybrid pricing become the norm, the limitations compound: fees that scale with your revenue, rigid pricing logic, and infrastructure you don't own or control.

Open source billing tools exist to fix that. And if you're building an AI product, an API-first SaaS, or anything where usage-based or credit-driven pricing is central to how you monetize, Flexprice is the most purpose-built option on this list. 

It handles real-time metering, credit wallets, entitlement management, and hybrid pricing models natively, without the revenue tax, without the lock-in, and without billing logic scattered through your codebase.

The best time to get your billing infrastructure right is before it becomes the thing slowing you down. If you're evaluating your options, start with Flexprice on GitHub and see how quickly you can get a working billing layer running.