Free Invoice Generator - A free invoice generator for startups
Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
Bookipi Invoice App - A minimal, beautiful invoice app for freelancers
Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.
Invoice.to - A simple & beautiful invoice generator with Stripe & Paypal
GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.