Invio is a web application for free and open-source billing, designed to focus on the essentials. While many tools try to be both a CRM, accounting suite, and project management platform, Invio takes a radical approach: it is a billing tool, period. You create your clients, generate detailed line-by-line invoices, mark them as paid, and send them.

A key feature distinguishes Invio: sending secure links to your clients, who can view their invoice without needing to create an account. No subscription, no per-invoice fees, no hidden costs — self-hosting ensures your data remains yours, safe from pricing changes or SaaS service closures.

Technically, Invio is built on a modern and lightweight stack: the Deno runtime, the Fresh framework for the interface, and Hono paired with SQLite on the backend. This simplicity makes it an easy-to-deploy and resource-efficient solution, ideal for freelancers and small businesses who want to bill simply and retain control over their data.