Minecraft is a game about placing blocks to build anything you can imagine. At night monsters come out, make sure to build a shelter before that happens...
Mincraft is a cross-platform indy sandbox game (written in Java) that allows you to create your own world. And my son is completely into it! It's not free but it is very reasonably priced (currently €14.95 while in beta, will be €20 once released). Having said that there is a free version (Minecraft classic) but it's not really used by anyone anymore. As I said my son is really into it and I have been helping him build a headless Minecraft server for him and his mates. I thought I'd make a TKLPatch for it and share the love. :)
Minecraft is not strictly open source in the usual sense of the word (as the source code is not directly available for download) but it does have a licence (see here) which allows decompiling and modifying (although not redistribution - see here). As such, once this patch is completed it will not include the actual Minecraft server software, but will download the official .jar. To be useful it will also need to check and update the .jar as required (server and client must be the same version for game to work). This will probably become less relevant once the game is officially released.
The dev has stated that once he has 'finished' it (and made 'enough' money out of it and moved onto something else), he will completely open source it. So until then, it probably does not quite qualify for release as a TKL appliance (only a patch) just yet. Despite the fact that the appliance itself will be completely open source. Once I have it finalised I will put it up on the TKL Community SourceForge project.
This patch is in development and will not be released until I have confirmed with the game dev that it complies with his licence and T&C (see links above).