Harmonix’s new game is a musical FPS called Chroma

Yes the Rock band and Dance Central series dev next game is a FPS with a different style, Chroma will be a musical FPS.”The hope is that music is meaningful to every moment of gameplay,” says Drake, laying out the game’s ambitions. Chroma is being developed in conjunction with Hidden Path, the studio responsible for Counterstrike: Global Offensive. source

Harmonix will be releasing a closed alpha at the end of February, you will need to sign up for it on the Chroma alpha site here. The game has only been in alpha for four months. They say the experience will be rough, but if you want to help out with the early stages sign up play try it out and see how much fun you can have.