It's pretty much what the title says: Doom running on a Texas Instruments Nspire graphing calculator. It's not the first example of geeks getting game code to run on these graphing calculators—people have been trying to cram Doom and Wolfenstein 3D into them for years—but this particular attempt looks insanely good.
Source: Kotaku
Can Doom run on Wii?
You can get Doom running on a graphics calculator but Capcom can't get Street Fighter IV or Marvel vs Capcom 3 running on a Wii? Really Capcom? Really?
Feats like this one just prove that there is a lot of untappped power in old hardware just waiting to be unleashed by clever developers.