Rainmeter is a customizable performance meter, which can display the CPU load, memory utilization, disk space, network traffic, time and many more things.
Features:
Freeform skins
Supports Windows transparency
Plugin system for 3rd party support
Anti-aliased drawing routines
Works also as Litestep plugin
Has ability to hide on mouse over
Can stick to the desktop (i.e. doesn't hide with Show Desktop)
Skins can react to mouse events
Multiple skins can be ran at the same time
Can be controlled from 3rd party applications with !bangs
and more...
Important: You need to download
gdiplus.dll to run Rainmeter if you don't have WinXP (or newer)