Receiver is a game (more of a tech demo really) that was made by Wolfire for the 7DFPS challenge. It's free if you've preordered Overgrowth, and it's $4.99 for everyone else (hint: buy Overgrowth!)

It's quite a unique little game, because every individual action that you make with your gun is controlled by a different key. For example, to reload, you have to eject the magazine, put it away, take out another, put it in the gun, and pull back the slide to chamber a bullet. Each of these actions are controlled with a button. There's a video of it on that website, check it out and if you like the concept, buy it (or Overgrowth)!