Topic on Talk:Bit.Trip Runner
Desura does not have its own DRM-free specific system, but it does have any account system from which you can download the games. Most of those do not use any DRM, and if they do, those are specific implementations created by the developer. The same thing is with the USC - I have an account and games, which can only be downloaded by that account. But if I wanted to, I can just copy most of the games and they will work on any Linux machine regardless of whether USC is installed.