Meteroid delivers the billing infrastructure that SaaS companies need when Stripe Billing gets too rigid and building in-house gets too expensive. The Rust backend ingests usage events via REST API or Kafka with deduplication by event ID and customer ID, storing time-series data in ClickHouse for sub-second aggregation queries across billions of events. Billable metrics transform raw events — API calls, compute time, tokens, storage, transactions — into accurate charges using configurable aggregation functions, dimensions, and filters without pre-aggregation. The plan builder supports any pricing structure: flat rate, per-unit, tiered graduated, tiered volume, package, and hybrid combinations with multiple price components per plan. Versioned plans enable pricing changes without affecting existing subscribers through grandfathering, while experiments let you A/B test pricing with controlled rollouts. Subscription management handles the full lifecycle — creation, upgrades, downgrades, mid-cycle proration, scheduled changes, and cancellation with configurable grace periods. The TypeScript frontend provides a complete web dashboard for managing customers, plans, subscriptions, invoices, and revenue analytics with MRR tracking, churn analysis, and cohort insights. Automated invoice generation handles complex scenarios including usage-based line items, credits, discounts, and tax calculations with PDF rendering. Stripe Connect integration enables payment collection directly through the platform. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Trusted by Mistral AI, PayPal, Groq, and Synthesia with over 10,300 GitHub stars and Y Combinator backing, Lago is the open-source billing engine that handles usage-based, subscription-based, and hybrid pricing models through a single API-first platform — replacing the need to build custom billing logic or depend on opaque SaaS pricing infrastructure. Real-time event ingestion via ClickHouse processes billable events with deduplication and multiple aggregation methods including count, sum, unique count, max, and weighted sum, while graduated pricing tiers, package-based billing, and percentage-based fees model any pricing strategy from simple subscriptions to complex marketplace commission structures. Automated invoice generation calculates charges according to configurable billing cycles with grace periods, proration for mid-cycle changes, and credit note issuance for refunds and adjustments. Prepaid credits enable pay-in-advance models where customers purchase credit blocks and draw down as usage accumulates, while entitlements tie feature access directly to billing plans for automated provisioning and de-provisioning. Payment orchestration integrates natively with Stripe, Adyen, and GoCardless with automatic retry logic, dunning workflows for failed payments, and multi-gateway routing. Revenue analytics provide cross-stream visibility into MRR, usage trends, churn, and revenue drivers through dedicated API endpoints. The customer portal embeds into your application for self-service invoice access and usage monitoring. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.

Kill Bill handles the complete subscription billing lifecycle from plan definition through invoice generation to payment collection across any gateway, with 15 years of Fortune 500 production use and 5,600+ GitHub stars behind it. Plans, trials, add-ons, and pricing tiers live in a versioned XML catalog that propagates changes without code deploys. The multi-phase subscription engine manages trial periods, promotional discounts, evergreen billing, usage-based metering, and hybrid pricing models with automatic proration on plan upgrades and downgrades. Automated invoice generation calculates charges, applies credits and adjustments, and triggers payment collection through pluggable gateways including Stripe, Adyen, Braintree, PayPal, and CyberSource. The Java plugin framework extends every billing domain with custom logic for tax calculation via Avalara AvaTax or Vertex, fraud detection through Accertify or Feedzai, and ERP integration without modifying the core. The Kaui admin dashboard gives finance and operations teams account management, subscription controls, invoice views, payment configuration, billing timeline visualization, MRR tracking, advanced search, and full audit history with object-level change tracking. Multi-tenancy isolates billing data across thousands of brands with tenant-specific catalogs, payment configs, and RBAC policies. REST APIs expose every operation with webhook notifications for downstream integration. Deploys via Docker Compose on MySQL or PostgreSQL. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache 2.0 licensed.

Flexprice is a developer-first billing platform built specifically for AI-native and SaaS companies that need usage-based, credit-based, and hybrid pricing models without building custom billing infrastructure. The metering engine ingests millions of usage events in real time through HTTP APIs or SDK calls, supporting sum, count, unique count, latest value, and multiplier aggregation strategies across custom event schemas like API calls, token counts, compute minutes, and GPU time. Credit management handles prepaid wallets with promotional grants, rollover caps, auto top-ups, and priority-based credit application during invoice generation. The pricing engine supports per-unit, tiered, volume, package, and flat-rate models with per-customer overrides, committed minimums, and enterprise contract terms. Feature entitlements enforce boolean toggles, metered usage limits, and configuration values per plan, enabling applications to gate functionality through simple API checks. Automated invoicing calculates charges from real-time usage data with proration for mid-cycle upgrades and downgrades, generating detailed line items linked to tracked consumption. The architecture separates event ingestion through Kafka from billing computation via Temporal workflow orchestration, allowing each layer to scale independently with ClickHouse handling high-performance usage aggregation. Stripe Connect integration processes payments and manages customer payment methods. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPLv3 licensed.

AI and API products live or die by usage, and OpenMeter is the open-source stack that measures it, rations it, and bills for it. Your application emits CloudEvents for every billable action; OpenMeter validates and deduplicates them, then aggregates usage in real time so dashboards and enforcement checks never wait for a nightly batch. Meters slice that usage by customer, time window, or any dimension you attach, which turns raw events into answers like tokens per workspace this month. Entitlements decide who gets what: metered allowances with balances and overage, boolean switches for features like SSO, and static JSON configuration for per-customer model access. Grants top allowances up once or on a schedule, resets roll balances over each usage period, and one API call tells your app whether a customer still has access right now. On the money side, plans carry flat, per-unit, tiered, package, or dynamic prices; subscriptions, credit balances, and the invoice lifecycle run alongside, with webhooks announcing everything to your other systems. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.

Used by Tailwind Labs and recognized as an official GitHub funding partner, Polar is the open-source billing infrastructure that lets developers ship production-ready monetization in hours instead of weeks. Meter tokens, API calls, agent runs, GPU seconds, and storage with event-level precision, then compose usage billing with subscriptions, seats, credits, trials, and discounts into whatever pricing model your product requires. As Merchant of Record, Polar handles sales tax, VAT, chargebacks, receipts, and regulatory compliance across all supported countries so you receive clean payouts without building tax infrastructure. Integrate via the full REST API with official SDKs for JavaScript, Python, PHP, and Go, plus framework adapters for Next.js, Astro, Remix, SvelteKit, and Laravel enabling checkout integration in minutes. Automatically deliver benefits upon purchase including GitHub repository access, Discord roles, license keys, file downloads, and meter credits through configurable automation rules. The built-in customer portal provides subscription management, payment method updates, invoice history, and benefit access with full white-label branding. Monitor revenue, costs, and margins through real-time analytics dashboards showing the unit economics every AI startup needs to scale. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache License 2.0 licensed.

With nearly 10,000 GitHub stars and over a decade of development since 2013, Invoice Ninja is the most complete source-available invoicing platform for freelancers and small businesses — combining professional invoicing, online payments, expense tracking, and project management in a single self-hosted application. The Laravel API backend powers a React web portal and Flutter native applications for Windows, macOS, Linux, iOS, and Android, delivering a consistent experience across every device. Create professional invoices and quotes with real-time PDF preview, product libraries, custom templates, and automatic tax calculations. Clients receive branded emails and access their dedicated portal at your custom domain to view documents, approve quotes with e-signatures, and pay with one click via Stripe, PayPal, Square, GoCardless, Authorize.net, Braintree, or Mollie. Recurring invoices with auto-billing charge saved payment methods on schedule — weekly, monthly, or annually — with automatic reminders and late fee calculations. The built-in project management suite includes Kanban boards for task organization, billable time tracking with start/stop timers, and vendor expense management with receipt attachments. Bank account synchronization via Yodlee or GoCardless automatically imports transactions for reconciliation. E-invoicing with PEPPOL network integration supports electronic invoicing standards for European and government compliance. Reports cover invoices, expenses, profit and loss, tax summaries, and aged receivables. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Elastic License v2.

SolidInvoice ships a complete billing platform as a single FrankenPHP binary — no separate PHP installation, no web server configuration, just one executable that delivers quote-to-invoice conversion, automated recurring billing, Stripe and PayPal payment processing, multi-currency precision arithmetic, and eight render-ready PDF templates out of the box. Maintained since 2012 across 63 releases with 30 contributors, the Symfony 7 and PHP 8.4 backend provides quote creation with one-click conversion to invoices, recurring billing with configurable frequency schedules, and online payment processing through Payum supporting Stripe, PayPal, and additional gateways. Multi-currency support uses real Money objects for precision arithmetic, while multi-tax support handles invoice-level and line-item tax rates with automatic calculation. Client management stores contacts, multiple addresses with map integration, credit balances, and complete quote and invoice history per client. The redesigned Tabler-based UI features a dashboard with hero statistics, ChartJS revenue trend visualization, attention-required alerts for overdue and draft invoices, quick actions, and a recent activity timeline. A RESTful API enables integrations with external systems. Multi-channel notifications deliver alerts via email, SMS, and webhooks. Google OAuth and two-factor authentication secure access. Grid export and full company data export support backup and migration. Deploy using Docker, Homebrew, the standalone FrankenPHP binary, or from source. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Hosting companies that sell VPS plans, game servers, or dedicated machines get a branded storefront, recurring billing, and a ticket desk from Paymenter, running on their own server. A customer browses a category, picks a free, one-time, or recurring plan billed every few days, weeks, months, or years, and shapes the order with select, radio, checkbox, text, number, or textarea options, some of which carry their own price. Prices can differ per currency, and a setup fee is optional. Payment runs through Stripe, PayPal, or Mollie, with tax rates and coupons set from the admin panel. Once it clears, a server extension for Pterodactyl, Virtualizor, VirtFusion, Convoy, cPanel, Plesk, DirectAdmin, or Enhance creates the service. A daily job issues renewal invoices, suspends overdue accounts, and terminates long-overdue ones. The customer portal covers services, invoices, and tickets in 24 languages, and tickets accept replies by IMAP email piping. Staff work with roles, audit logs, email logs, and notification templates, while API keys and OAuth clients connect outside tools. Optional extensions add an affiliate program, announcements, and Discord alerts. Moving over from WHMCS takes one built-in command that imports clients, products, services, tickets, and invoices from a copy of your database. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Hosting companies sell, invoice, provision, and support hosting, domains, SSL certificates, and VPS servers from PNLCS, a free self-hosted billing platform with one client portal at the center. Customers browse your catalog, configure services, apply coupons, and check out, and the moment an order is paid a server module creates the account or machine on Panelica, cPanel, Plesk, DirectAdmin, HestiaCP, Proxmox VE, or Vultr. Renewals then run themselves: invoices are generated ahead of the due date, stored cards are charged with retries, reminders and late fees follow, and unpaid services suspend automatically and restore themselves once payment lands. Domain registration, transfers, renewals, WHOIS and EPP codes, and SSL issuance run through the same checkout, while customers manage their actual hosting from the portal itself, including files, mailboxes, databases, FTP accounts, subdomains, DNS records, cron jobs, and backups. Eight payment gateways share one engine, so partial payments, refunds, and credit balances behave the same everywhere. Support tickets route by department with priorities and attachments, a searchable knowledge base deflects repeat questions, and affiliates track referrals and commissions. Operators get revenue dashboards, client management with impersonation, bulk invoicing and mail, and twenty-seven reports covering income, MRR, churn, domains, and tax, all in thirty languages and sixteen themes. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.

Hyperswitch from Juspay delivers the most comprehensive open-source payment orchestration stack available — a Rust-built platform that connects to Stripe, Adyen, Braintree, Worldpay, Checkout.com, Cybersource, and 120+ payment processors through a single API integration. Intelligent routing drives each transaction to the processor with the highest predicted authorization rate using rule-based, volume-based, and machine learning algorithms, while seamless failover and automatic retries recover revenue from declined transactions using 30+ parameters including decline codes, card BIN, transaction size, and region. The PCI-compliant card vault stores payment methods securely in a dedicated service separate from the main application server, and the reconciliation engine automates 2-way and 3-way matching with backdated support, staggered scheduling, and customizable audit-ready outputs. The Control Center dashboard provides visual workflow builders for routing rules, payment analytics, and operations management. Cost observability tools drill into scheme, interchange, and acquirer fees to detect anomalies and optimize processing costs. The modular architecture allows deploying individual components — routing, retries, vaulting, observability, or the full suite — without vendor lock-in. The web client SDK collects payment information with prebuilt UI components and supports WooCommerce integration. Deploy via Docker Compose with the app server, control center, card vault, and PostgreSQL. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. Apache-2.0 licensed.

BTCPay Server processes Bitcoin payments with zero transaction fees, zero monthly costs, and zero third-party custody of your funds. Payments settle directly from customer to your wallet through a full Bitcoin node that provides cryptographic proof of receipt without trusting any intermediary. Lightning Network integration through LND, Core Lightning, or Eclair enables sub-second confirmation at sub-cent fees, with Ride The Lightning providing web-based node management within BTCPay itself. The Point of Sale app creates storefronts with product catalogs, tipping, and QR code displays for physical retail, events, or web embeds. Hardware wallet support through BTCPay Vault connects Ledger, Trezor, and ColdCard for transaction signing, keeping private keys in cold storage while running a hot payment interface. Multi-tenant architecture allows multiple stores on one instance, each with isolated wallets, Lightning nodes, and user permissions. The Greenfield REST API exposes every function programmatically for headless operation, automated invoicing, and custom integrations. E-commerce connectors for WooCommerce, Shopify, Magento, and PrestaShop plug in alongside Zapier for workflow automation. Optional Tor hidden services expose the instance as an onion address for censorship resistance. The official Docker Compose stack handles Nginx reverse proxy, Let's Encrypt TLS, and optional Tor configuration on a dedicated RepoCloud VPS with guaranteed CPU, RAM, and SSD. MIT licensed.

Roughly 40 integrated business apps forming a full ERP: Odoo's open-source suite runs companies end to end. The Community Edition, licensed LGPL-3.0, ships roughly 40 apps covering CRM, sales, invoicing, basic accounting (journals, chart of accounts, taxes, reconciliation), inventory and warehouse management with multi-step routes, manufacturing with BOMs and work orders, purchasing, project management, timesheets, HR, a website builder, and eCommerce. Each app works standalone, but they share one PostgreSQL database and one data model, so a confirmed sale updates stock, triggers procurement, and posts invoices without integration glue. The modular design means you enable only the apps you need and extend with 40,000+ community modules from the Odoo app store covering nearly any vertical requirement. Inventory supports multi-warehouse stock, reordering rules, and lot and serial tracking with barcode-ready operations; manufacturing ties BOMs, work orders, and work-center routing directly to sales demand and stock levels; and the website builder sells straight from your product catalog with payment provider integrations. You can start with just CRM and invoicing on day one and switch on inventory or eCommerce later - new apps integrate with existing data instantly because the schema is shared. The server is Python with an XML/JavaScript view layer, and because data lives in plain PostgreSQL there is no proprietary format: you can query, back up, migrate, and extend business data directly, with unlimited users and no per-seat licensing - where enterprise ERP pricing is per user per month, headcount here costs nothing.

Bigcapital gives small and medium businesses a complete double-entry accounting, invoicing, and inventory management platform they can self-host for free, replacing the per-seat subscriptions of QuickBooks, Xero, and Wave. Every transaction records debits and credits across your chart of accounts, automatically generating balance sheets, profit and loss statements, trial balances, general ledger reports, journal entries, accounts receivable and payable summaries, cash flow analysis, inventory valuation, and inventory summary reports. Sales invoicing supports recurring schedules, customer payment tracking, estimate-to-invoice conversion, and configurable GST/VAT tax rates. Purchase invoicing handles vendor bills with expense categorization for payroll, rent, and operational costs. The inventory module tracks stock levels using FIFO and average cost methods, automatically adjusting quantities on every sale or purchase and providing reorder alerts. Multi-currency accounting converts transactions at real-time exchange rates and consolidates them under customer or vendor profiles with detailed currency reports. The platform deploys via Docker Compose with multi-tenant isolation giving each organization its own separate database, requiring as little as 2GB RAM for the complete production stack. A headless REST API with Postman collections lets developers embed the accounting engine into external applications for programmatic transaction management. Role-based permissions control access for team members and invited accountants across organizations. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. AGPL-3.0 licensed.