Desktop app Konfabulator keeps little programs called Widgets running on your Mac or Windows desktop.
Konfabulator's been around for quite some time, and it was so good Apple included the very Konfabulator-like Dashboard in their latest OS X release. Technically Konfabulator's a "Javascript runtime environment," which doesn't sound very exciting, but the widgets (Javascript apps) that Konfabulator runs are useful and good-looking. Some example widgets pictured from left to right in that teensy screenshot above: a monthly calendar; the 6-day weather forecast for your zip code; an iTunes remote; a computer memory usage monitor; a great big Recycle Bin; and a picture frame that rotates photos from your library. Perfect for Windows users with Tiger Dashboard envy, Konfabulator's free to try, 20 bucks for a single-user license, and works on Mac OS X or Windows.