Slightly related, many fast-food restaurants are also ran on Linux (back-end server in the restaurant, the registers that connect to them, etc.).

Taco Bell's system runs on "Taco Bell Linux" (or did, anyways, 10 years or so ago). I have a copy of their CD installation discs somewhere, I meant to look into it to see what distro they were building on top of but I never got around to it.