GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.
Ledger-cli.org - Ledger is a powerful, double-entry accounting system that is accessed from the UNIX command-line.
YouNeedABudget - Personal home budget software built with Four Simple Rules to help you quickly gain control of your money, get out of debt, and reach your financial goals!
Teamleader - CRM, invoicing & project planning in a single tool for SME's
Money Tracker Pro - K-Tech Systems - experts in the world of .Net
Free Invoicing Software - Free Invoicing Software provides the facility of online billing.