A credit-card sized inexpensive (less than 40USD), versatile computer by the RaspberryPiFoundation.  Ideal for education, experimentation and easy-entry home-grown embedded devices.  You can make a media player that hangs off its own video lead behind the back of your TV.

See http://raspberrypi.org

The operating system is a LinuxDistribution on an SD card which makes it easy to have different versions and swap them over.
----
CategoryHardware