Konfabulator is very cool!

[Paul Bernhardt]

A javascript programing environment for which hundreds of 'desktop 
widgets' have been written. 

For OSX only.

Some duplicate in much prettier style existing functions, such as Airport 
signal strength, battery reserve, a lovely clock. 

Others are very handy/fun. A weather update, stock ticker, Simpson's 
quote generator, news gatherer, etc.

Check it out!

http://www.konfabulator.com/

Paul