Catacomb Snatch
Made for the Humble Bundle Mojam in 60 hours. The other games made in the 60 hours were Fists of Resistance and The Broadside Express. The game is not Open Source or Free/Libre Software, but the source code has been released.
Availability
The game was originally only made available to those who purchased the Humble Bundle Mojam, but other versions are available that work on the original source code to improve the experience, such as Uber Catacomb Snatch and the fork available on CatacombSnatch.net. The original source code has also been released for everyone, although the license of the code is not specified.