GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.
Odoo - An all-integrated business app suite to unleash your growth potential.
Synder - AR Automation
ERPNext - The ERP Software that helps you take full control of your business. ERPNext is both powerful and easy to use.
Xero - Xero is online accounting for your small business.
PracticePanther - PracticePanther offers CRM, invoicing, time tracking and communication solutions for law firms.