I downloaded this a few hours ago and I am very much in love with this game. You play as a wave of light, controlling the vibration and wavelength with the mouse. It's one of those games that is very easy to understand and play, but takes a huge amount of skill to play well, especially once multiple light colors, reflecting mirrors, and wormholes that warp you around the screen come in to play.
It's on steam, there's a free demo, and I can't recommend it enough. Here's a trailer if you're curious (dat music!).