Open Source Invoice Software
An invoice is a legal record of money owed, but many hosted tools treat it as a metered event, charging per invoice sent or per seat while quietly sitting between you and your customers' payment data. That framing is worth resisting, because billing is where a small business is most exposed to lock-in: your client list, tax history, and payment references are the last things you want trapped in someone else's schema. Open source invoicing keeps the templates, customer records, and payment history on infrastructure you run, connects to the payment gateway you already use, and exports cleanly, so getting paid never depends on a pricing 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
Our picks
Four tools, from simple invoicing to full usage-based billing.
Best for freelancers and small businesses: SolidInvoice SolidInvoice handles the everyday billing cycle cleanly: one-click quote-to-invoice conversion, recurring invoices, multi-currency amounts modeled as real money objects, and branded PDFs. Payments run through your own Stripe, PayPal, or other Payum gateways with no card data on your server. The same codebase runs self-hosted for free or as a paid hosted service.
Best for usage-based billing: Lago Lago is API-first billing infrastructure for teams that charge by consumption. It meters usage events in real time and supports usage-based, subscription, and hybrid pricing, with prepaid credits, coupons, dunning, and revenue analytics on top. It is payment-agnostic, working with Stripe, Adyen, GoCardless, or any gateway, and self-hosts via Docker Compose when you want the data on your own infrastructure.
Best for subscription billing at scale: Kill Bill Kill Bill runs subscription billing and payments in your own infrastructure with no per-transaction fees. It covers multiple billing models, trials, usage metering, wallets, and prepaid credits, with native Stripe, Adyen, Braintree, and PayPal integrations and the Kaui back-office UI. A plugin framework, multi-tenancy, and RBAC make it a fit for teams that outgrow a simple invoice app.
Best free invoicing with mobile apps: Crater Crater pairs a Laravel and Vue web app with React Native apps for Android and iOS, so you can invoice from a phone. It covers invoices, estimates, expenses, recurring invoices, and multiple companies, plus a customer portal with Stripe payments and white-labeled invoice and email themes.
What to weigh before you pick invoice software
Your billing workflow, not the feature grid, should decide the shortlist. A freelancer sending one-off invoices with a PDF and a payment link needs something very different from a company metering usage. If you send simple quotes and invoices, SolidInvoice and InvoicePlane cover quote-to-invoice conversion, recurring schedules, and multi-currency PDFs without extra machinery. If you bill for consumption or subscriptions, Lago and OpenMeter are built to meter events and generate invoices from them, which is a different category of tool wearing the same label.
Then decide where money movement and accounting live. Good invoicing makes it obvious when an invoice is issued, viewed, paid, refunded, or written off, and records gateway events back against the right invoice. Most tools here connect to Stripe or PayPal, and Kill Bill and Crater record payments cleanly against invoices. Decide early whether the invoicing tool or a separate ledger is your source of truth, because LedgerSMB and Frappe Books are full double-entry accounting systems rather than plain invoice generators, and running two sources of truth for the same customer creates reconciliation work.
Finally, treat data control as an operational choice. Invoice records hold customer contacts, tax IDs, line-item pricing, and payment references, so permissions, backups, and a tested restore matter more than they do for a task board. A solo shop may be fine with a single-tenant install; an agency needs role-based access and email delivery logs. Whatever you choose, confirm the exit up front. Customers, invoices, line items, taxes, and payments should export as CSV or another documented format, with the PDFs your customer actually received preserved alongside them.
Related categories
Frequently asked questions
Does open source invoice software replace accounting software?+
Usually not, and conflating the two causes trouble. Invoicing handles creating invoices, collecting payments, and tracking balances; accounting manages the general ledger, reconciliation, and financial statements. Some tools cross the line: LedgerSMB and Bigcapital are double-entry accounting systems with invoicing inside, and Frappe Books keeps the full books offline. Decide which system owns customers, revenue, and taxes before go-live so you are not maintaining two conflicting records.
Which tax features should I look for?+
Look for configurable rates, tax-inclusive and tax-exclusive pricing, customer tax IDs, exemption handling, and line-level versus invoice-level tax behavior, plus reports that match how you file. If you sell across jurisdictions, confirm the tool applies multiple rules without hand-editing every invoice. SolidInvoice models money and tax rules explicitly rather than as free text. The software does not remove your compliance duty, so run real invoice examples before relying on it.
How do online payments get recorded against an invoice?+
Most tools connect to a gateway, then write payment events back onto the invoice. SolidInvoice routes payments through Stripe, PayPal, or other Payum gateways with no card data touching your server, and Crater and Kill Bill mark invoices paid from gateway callbacks. Check that the integration handles refunds, partial payments, and failed charges, and remember a paid flag still has to match batched bank payouts during reconciliation.
What matters if I bill clients on subscriptions or retainers?+
Recurring billing is more than copying an invoice each month. Check for schedules with start and end dates, proration, automatic sending, and payment retries. UniBee and Kill Bill are built around subscription lifecycles, covering create, update, cancel, trials, and discounts, while Lago and Flexprice add usage metering and prepaid credits for retainer-style balances. If these are weak, you will spend more time correcting invoices than the automation saves.
Can a team use it without everyone seeing every client?+
That depends on the permission model. Smaller tools may only offer admin and standard roles, which is risky when contractors should see limited data. InvoiceShelf is multi-tenant with member invitations and custom roles, and IDURAR ships role-based access as part of its ERP model. Look for client or project scoping and logs of who created, sent, voided, or marked an invoice paid before trusting sensitive pricing to a shared login.
What is the difference between invoicing tools and usage-based billing platforms?+
They solve different problems. Invoicing apps like InvoicePlane, Crater, and SolidInvoice create documents for work already done. Billing platforms like Lago, OpenMeter, Flexprice, and UniBee ingest usage events from your application and turn metered consumption into invoices in real time, through SDKs and webhooks rather than a manual create-invoice screen. If you sell per-seat services, pick the former; if you sell by API call or consumption, pick the latter.
How hard is it to bring over existing customers and old invoices?+
Customer imports are usually straightforward from a clean CSV of names, addresses, tax IDs, and currencies. Historical invoices are harder, because line items, taxes, discounts, and payments rarely map one to one between systems. A common approach is to import open invoices and customers, then keep older invoices as archived PDFs or read-only records. TaxHacker can even extract fields from old invoice images if you are starting from scans.