It's an embedded OS

Okay, we are getting into some really techy stuff here. Linux is also used in many ``embedded applications''. An embedded application is simply the use of a computer in a machine that serves purposes other than that of a usual computer.

For example, many low-end consumer-grade routers use Linux as an operating system. Other specialized devices utilizing Linux include ceilometers (machines to measure cloud height), robots, and many projects at Lawrence Livermore National Lab and other high-end research facilities.