Arena Live is now released as a browser game only for Linux OS and Firefox browser.
Arena Live is the free Quake3 Clone Open Arena, based on ioQuake3 engine, an extendend version of the id tech 3, with less bugs and more added features. Open Arena comes with own built content like new textures, models, maps, weapons, and sounds.

In the future Arena Live will support other OS. For playing you need a quick registration on the site. It´s more like a demonstration and experiment i guess, haven´t tested it by myself.

Source: (german IT site)