GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.
Teamleader - CRM, invoicing & project planning in a single tool for SME's
Ledger-cli.org - Ledger is a powerful, double-entry accounting system that is accessed from the UNIX command-line.
FreshBooks - The ideal accounting software for small business owners.
InvoiceLion.com - Web based open source time management and invoicing software
Homemoney - HomeMoney: free service for planning of personal budget, family budget, small business budget. Possibility to reduce expenses and budget planning, accounting for small business.