I'm as grumpy about April Fools as the next games writer, but I'm happy with its bedfellow, Make Frivolous Fun Things Day. For example, were it not for MFFT, we would haven't SUPERQOT, a standalone Quake 1 modifcation that bundles SUPERHOT's [official site] time-moves-when-you-do mechanic into Id Software's age old first-person shooter. It's free to download with trailer and brief impressions below.
Now you know that you only need to call the developers of SUPERHOT in order to receive their game.
The original SUPERHOT prototype was a tight-as-dynamite twist on first-person shooter mechanics which turned gunfights into elegant ballets where you could dodge bullets, and into a strategy game where positioning, and the order in which you tackled enemies, decided your success or failure. It's now being turned into a full-game with, I'm told, a robust set of scenarios that take full advantage of that mechanic.
By comparison, SUPERQOT is a bit janky, since Quake's grunts, Death Knights, Scrags and Ogre's were never designed for real-time-with-pause combat. Still, it's fun. There's a single tip-ex'd level with sixty enemies to prance your way around, and it's a fair challenge given the number and relative strength of the enemies you're facing. Also I couldn't tell what a lot of the all-white pick-ups were, so I was probably missing out on a lot of health packs.
Quake 1 is open-source, which means everything you need to run this is bundled in the download. Scroll down a little on this page to find the download link.