Konfabulator is a program that allows users to add widgets to their Windows desktop. Originally released on the Macintosh, Konfabulator 1.8 now gives Windows users the ability to make use of the hundreds of Konfabulator widgets.
With Konfabulator, developers can make pretty much anything they would like with it. Popular widgets include weather monitors, stock tickers, to-do lists, clocks, calendars, and many other assorted "mini-programs".
The shareware version is free to try. It's $25 to register.
Download: Konfabulator Website