These past few months I joined the Ludum Dare Paris event twice. The idea is to create a game in 48 hours (about 20 hours of work).
During Ludum Dare #29 I joined Damian to create a Flash/Unity dual game: Happy Fishing. Basically the idea was to make two games, and have them communicate locally in a web browser, one game created with Flash, and one with Unity. One would be in 2D, and one in 3D. Result was unimpressive, but we got a medal in Innovation anyway! Crazy. More infos on Damian's Happy Fishing blog post.