My business card is a Nintendo DS cartridge. Plug it in, play a short game, find my contact info at the end. Wrote the whole thing in C, no game engine.
Built against the NDS SDK on bare-metal ARM9/ARM7. No OS, no game engine, just direct hardware registers. The top screen runs an animated bar chart; the bottom shows my contact info.
Works on any DS or DS Lite with a flash cart. Hand someone the cartridge and they plug it in like a regular game.