A 100% compatible replica of the famed SB 1.0 sound card. 8-bit ISA card. Full bill of parts. Even has a hex dump which turns an Atmel 89S51 into an 80C51 DSP chip (if you don't feel like buying one from China).
CC-BY-SA v4.0.
An opensource version of the C-64 game Paradroid. Also, there is an RPG fork of the game (FreedroidRPG).
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 freeware utility which clones most any hard drive block by block to another device. Possibly crypto agnostic.