I've just added what I'd probably call experimental level support of the Occulus Rift to my game Kairo. I've just released a patch so anyone with the Steam version of the game will be able to activate Rift support from the settings menus.
I've not yet recompiled the demo versions of the game with this support in, but I'll get that done in the next couple of days. So everyone will be able to try it out without having to buy the game.
I put a fair amount of time into getting this working, an especially large amount of time rebuilding how my GUI was done, but I don't really consider it complete yet. However a lot of people had been wanting to try it out so I figured I'd release it as it stands now and take feedback to make improvements.
[edit: Rift support is currently only available for the PC and Mac versions of the game]
Steam Link: Kairo