Minecraft maker Mojang (really, Markus "Notch" Persson) was working on a first-person shooter with another company, but that has now been officially canceled. Gone before you could get excited about it. Fortunately, this project was only in the prototype stage before it got canned.
Notch told Joystiq that the project was killed because "Mojang did not want more external dependencies." Also: "The success of Minecraft meant we could focus on projects fully owned by us."
Notch is open to future collaborations as long as they're not to make money. What a guy!
What a shame, though. I'm sure we all would have loved to see this FPS.