Update (Nov 2010): I have not worked on Foxden for over a year. I do not recommend you use it.
Foxden is a Firefox extension that allows you to tile all the web applications you use on one page. Imagine being able to see your email, your calendar, your bug tracker, feeds, twitter, whatever you use, on one page. Take a look at my setup:
As you can see, I have (counter clockwise from top left) my email, calendar, feed reader, todo list and a local text file for taking notes.
It’s free, should work wherever Firefox 3 works, and it could be yours right now.
Download the Foxden Firefox extension