Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
ERPNext - The ERP Software that helps you take full control of your business. ERPNext is both powerful and easy to use.
Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.
Odoo - An all-integrated business app suite to unleash your growth potential.
GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.
OCTO ERP - All-in-one platform to track and manage everything about your business. It's an ERP, CRM, and BMS combined at an affordable rate for businesses of any size. RFID, barcode, GPS, NFC and IoT built-in functionalities out-of-the-box.