For now, there's not that much choice here. The only game you can play is Traces of Illumination. While some people find this game great fun and highly addictive, others might be a little confused about the competetive nature that the original game concept inherently has. Well, I have good news: That's only where it starts. You can play this game in a competetive style if you wish, and there will even be contests (but that's just to have some kind of exciting event). However, if you want to experience the higher levels of Traces of Illumination, you'll have to consider collaborating with the "opposing" teams.
Also Traces of Illumination has a deliberate electro-tech-style that sure is not for everyone. You can either play Traces of Illumination here on the Web, in your Web browser - or download the standalone game. You just need to download and unzip the version specific to your operating system, unzip it and start the exe / app (no installation required).
There is currently a single-player evaluation version for unregistered players - but if you register you can play the multiplayer version and also save your high-scores. To get an idea of what the game looks like in action check out the first Traces of Illumination Screencast, which gives you a nice overview of the status at version 0.88 (but keep in mind: this is my first Screencast ever, so don't expect too much):
Traces of Illumination Screencast 01 - High Quality (800x600, 4000kbps)
Traces of Illumination Screencast 01 - Low Quality (400x300, 700kbps, not recommended)