GnuCash - A personal and small-business financial-accounting software, licensed under GNU/GPL and available for Linux, Windows, Mac OS X, BSD, and Solaris.
TopTracker - Beautiful, free time tracking
Ledger-cli.org - Ledger is a powerful, double-entry accounting system that is accessed from the UNIX command-line.
timeBuzzer - timeBuzzer enables freelancers and project-driven teams to track their time at the touch of a button, understand where their time goes and create reports with just a few clicks.
Free Invoicing Software - Free Invoicing Software provides the facility of online billing.
Cattr - Cattr is a free open-source self-hosted time tracker with desktop clients for windows, mac, linux.