konfabulator

Konfabultor is cool, I use it on Mac OS-X. Mostly the weather, cpu usage, mini to-do, calendar, pop-up reminder, and occasionally a floating itunes controller. Its cool, worth the dollars...

BUT- Mac users don't run out and get it if you plan on going into tiger:
http://www.apple.com/macosx/features/dashboard/

Samething, different name (sort of M$ish of them on this one- even call them widgets)