What tx says is funny. The site is absolutely simple.
I love it though. I just started learning html and javascript last week and now this thing provides an instant compiler. I change the border size on a table and, BOOM! Right when I finish typing the border shows up with the correct size. I see what it looks like instantly and can change what I want when I want. There isn't any clicking, switching windows, sftp-ing, downloading software, or anything.
It's simple and I love it. Since it handles Javascript I now have an instant way to deploy simple functions and tables. I can figure some useful relation, put it up using html and Javascript, and suddenly anyone anywhere has easy access to my results.
This thing also provides an instant way to write and test content for Google Gadgets, something even more useful than the editor Google provides.
And I think the design is clean, nice, and simple.