Cool open-source applications

Was looking around for some open-source applications for my Mac & found 2 cool apps -

• Cashbox - A great & simple tool to maintain your personal accounts. Switched from my Text files immediately. Needs more work on reports and export facility, but can work with it for now.
• Freemind - A cool tool, something even I was thinking of creating, for putting down my ideas in a structured form (but in a quick and simple way).

The more I search, the more better software I find for my Mac :) giving me more & more reason, to never think of going back to my PC.