Conky is a system monitor for X originally based on the torsmo code.
Since its original conception, Conky has changed a fair bit from its predecessor. Conky can display just about anything, either on your root desktop or in its own window. Conky has many built-in objects, as well as the ability to execute programs and scripts, then display the output from stdout.
Can be run on all POSIX (Linux/BSD/UNIX-like OSes).