SoapQuest1024 is a small written after reading "20 Open World Games" on Gamasutra and coming across "Adventure". It's a very simple tile-based game written in 1024 lines of Java. You can wander around the place, picking things up and using them on other things by walking into them. You can save the gameand go back to it later. It's fully data-driven, based on a simple CSV format, and has things like wandering treants and a day/night cycle with light calculations.
While Performous might be classified as a karaoke program, it is actually much more than that. Instead of just displaying the lyrics, notes are also displayed, and the performance is scored based on how well you actually hit the notes. Unlike in many other games in this genre, you will also see the pitch that you are singing, so you can see what you are doing wrong and easily (well, everything is relative) correct your pitch.