Rainmeter is a system modification tool for Windows PCs. It installs an overlay menu on top of your desktop that shows useful information about the state of your computer, among other things. There are a few themes that come built-in with Rainmenter. My favorite was Gnometer, which is a very easy-on-the-eye bar with a dark background and easily readable text. The other theme, Enigma, is a much more complete informative tool, but I found that it didn't work for me. Because it had too much information on-screen at all times. This is of course all about personal choice. Both themes are very well achieved and very useful.
By default, Gnometer installs a dark horizontal bar at the top of the screen, which contains floating gadgets. There were 4 gadgets installed at first: calendar, drives, recycle bin, and system. The drives gadget shows free space on your hard drives, the recycle bin shows the space of your trash bin and the system gadget shows your CPU ussage, RAM, and SWAP. You can of course add other gadgets. I ended up adding a weather gadget powered by MSN weather.
You can add new gadgets to both themes from the tray icon. Switching between themes seems to erase your settings, so you have to start configuring again. It takes a bit for themes to switch.