Kashoo - Kashoo mobile and online accounting software for small business. Cloud based system for invoicing, expense tracking & bookkeeping. Free Trial.
Invoice Ninja - Invoice Ninja is a free, open-source solution for invoicing and billing customers.
Akaunting - Free, open source and online accounting software for small businesses and freelancers
Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.
Commerce Sync - Commerce Sync automates the transfer of sales information to accounting software, populating any QuickBooks or Xero account.
GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.