An opensource version of the C-64 game Paradroid. Also, there is an RPG fork of the game (FreedroidRPG).
An application that lets any laptop act as a DJ console. With it, you can mix audio files in many formats.
An open source utility for Windows (32 and 64 bit) that will securely erase files and directories on a Windows machine, in addition to scrubbing free space and OS-related temporary files that could leak information. It can even wipe an entire system if you need it.
An open source clone of the game Worms in which you manipulate a team of characters (usually earthworms) to box, pummel, blow up, and otherwise mangle the characters of the other team in a cartoon-like fashion. Network/deathmatch play possible.
A website that lets you search out and download missing .dll files to fix a botched reinstall or application upgrade.
Somebody cloned Portal into an open source game done entirely in ASCII. Cute.
A realtime strategy game in which you compete in a virtual space with others to build the biggest, most robust network you can while attempting to compromise or crash the networks of rival system admins. It sounds a little like Starcraft meets Neuromancer with a healthy dose of the movie Hackers thrown in for fun. Runs on Windows as well as Linux.
Possibly the best collection of audiovisual CODECs for Win32 and Win64 out there. Widely reputed to have no malware or spyware hidden anywhere within.