The original Soundodger was an ace browser game (opens in new tab) that tasked you with avoiding a bunch of triangles to a rad selection of music, from the likes of Disasterpeace (Fez), Lifeformed (Dustforce) and Austin Wintory, who provided the excellent score for Journey. Now, developers Studio Bean have stuck a + on the end and transported the game to Steam. In doing so they've added new tracks, controller support, a level editor, and the ability to generate new tracks based on your MP3s.
I sense you may need some sort of video to get better acquainted with this Geometry Wars-esque anti-shooter, so I've stuck the launch trailer below. The game's masterstroke is its seamlessly integrated slo-mo button, which fits with pretty much any track thrown at it (except perhaps for John Cage's 4'33).