This is a 2D online 'game' I made in 2005. There aren't really any goals, you just wander around and build stuff in an infinite world. Other users can see the changes you make after you save them. There are a lot of design decisions that I would make different now, but it's a neat concept, and pretty addictive for a few days until you get tired of the goallessness.

There are two versions with their own sets of data (world definitions, terrain chunks, users). You can play around in the original one. I have yet to get the later version working on here (need to clean up PHP scripts), but it is planned. The later version has larger rooms (64x64 instead of 16x16), and replaces the ability to dig holes into the ground with the ability to place teleporters between any 2 points, among other things.

There's also a totally outdated sourceforge page about it.