Kometen is yet another example of an indie game that's hard to really define as a "game", and instead, is more of an interactive experience with fantastic art and music wrapped around a vaguely game-like wrapper.
In Kometen, all you do is play as a comet and explore the galaxy. You can't lose, you can't die. You navigate about by tapping on various planets to orbit them. Some planets have space junk also orbiting that you can munch up to briefly speed up. That's really all there is to it.