Apparently there is a brand of keyboards that includes a tiny display in each individual key -- the Optimus Maximus is one of them. This allows you to program them to display whatever you'd like, so Doom had to be the obvious conclusion to that madness.
The display size for each key is around 48x48, so be prepared to guess exactly what is going on with each frame of this video. I've watched it a couple of times and, apart from this being a mod with different sound effects, I'm guessing the player is shooting at enemies from memory alone.
via destructoid http://ift.tt/2hGUSlB