Doom runs on a lot of things. Here it is on an Intel Edison chip, which is actually quite mundane as these things go; far more impressive is seeing it in action on a home pregnancy test, 100 pounds of moldy potatoes, the display that shows your order in a restaurant, and even some sheep in Minecraft. Here's a whole separate list if you really want to go down that rabbit hole.
The most recent addition to the lineup of "weird things running Doom" is nothing less than Twitter, and specifically the Tweet2Doom bot that enables anyone with a bit of patience to play the game directly through the social media platform. Movement and interactions are handled through a basic scripting language that's input via reply tweets sent to the bot; those instructions are converted into a gameplay video that's sent to the user in a tweet. Each valid tweet also generates a "new game state" that can be extended through further replies, meaning that gameplay sessions can be extended across tweet threads.
The process is simple, although there are a few syntax rules and you'll need to be patient enough to figure out how the scripting works. To start a new game, you must reply-tweet "/play x,,e,,e,,e,,50-,50-u,15-f," for instance. Okay, so maybe it's not that simple.