Open Source Invoice Software
An invoice is a legal record of money owed, yet many hosted tools treat it as a metered event - charging per invoice sent or quietly sitting between you and your client's payment data. The open source options here put the invoice templates, client list, and payment history on infrastructure you run, so getting paid never depends on a per-seat tier or a processor's goodwill.
Lago
Open-source billing infrastructure for usage-based, subscription-based, and hybrid pricing models
IDURAR
Self-hosted ERP and CRM for invoicing, quotes, accounting, inventory, and HR
Crater
Open source invoicing app for tracking expenses, payments, invoices, and estimates
TaxHacker
Self-hosted AI accounting for receipts, invoices, and transactions with custom prompts and categories
Kill Bill
Open-source subscription billing and payments platform with real-time analytics and financial reports
Frappe Books
Desktop accounting for small businesses, works offline with local storage
Bigcapital
Accounting and inventory software for small and medium businesses
Flexprice
Open-source billing infrastructure for usage-based, credit-based, and hybrid pricing
InvoicePlane
Self-hosted invoicing app for managing invoices, quotes, clients, and payments