“GnuCash is personal and small-business financial-accounting software, freely licensed under the GNU GPL and available for GNU/Linux, BSD, Solaris, Mac OS X and Microsoft Windows. Designed to be easy to use, yet powerful and flexible, GnuCash allows you to track bank accounts, stocks, income and expenses. As quick and intuitive to use as a checkbook register, it is based on professional accounting principles to ensure balanced books and accurate reports.”

http://gnucash.org/

SQL-Ledger is a multiuser, double entry, accounting system written in Perl. Data is stored in a SQL server, display and data entry is through a GUI or text based browser. The entire system is linked through a chart of accounts. Each item in inventory is linked to income, expense, inventory accounts and tax accounts. When you purchase and sell goods and services the accounts are automatically updated.

http://www.sql-ledger.com/

a suite of tools and applications for solving the needs of the enterprise. From human resources, accounting, customer relationship management and project management to supply chain or e-commerce, GNUe can handle the needs of any business, large or small.

GNUe is a development framework that enables enterprise information technology professionals to customize applications for their businesses. The GNUe platform boasts an open architecture and easy maintenance. It gives users a modular system and freedom from being stuck with a single-source vendor. Plus, users get consistency and the ability to tap into a network of best practices from other enterprises, saving valuable development time.

http://www.gnuenterprise.org/sections.php?op=viewarticle&artid=24

Compiere is the Open Source ERP & CRM business solution for the Small-Medium Enterprise (SME) in distribution and service.

http://www.compiere.org/