Invoice Ninja

Invoice Ninja is a source-available billing and invoicing platform built with PHP and the Laravel framework. It lets freelancers and small businesses create branded invoices and quotes, accept online payments through gateways like Stripe, PayPal, Square, and GoCardless, and manage the full client billing lifecycle from a single self-hosted instance.

Beyond invoicing, it bundles project management, billable time tracking with Kanban boards, expense and vendor tracking, purchase orders, recurring invoices with auto-billing, and a branded client portal where customers can view and pay invoices. It integrates with hundreds of external services via Zapier, Make, and Pabbly.

A typical deployment runs the Laravel app against a MySQL/MariaDB database, making it well suited for organizations that want to keep financial and client data on their own infrastructure rather than a hosted SaaS. Note that it is licensed under the Elastic License 2.0, which is source-available but not OSI-approved open source.