Conky is a free software system monitor for the X Window System. It is available for Linux, FreeBSD, and OpenBSD
I like Conky and use it a lot, I mainly use it to monitor my CPU, RAM, Disk and Eth.
But some others use it with Xmms to check which tune is being played, to check the weather and a lot more things.
Here is an example of how a Desktop may see with Conky enabled.
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