This is a wonderful tool. It's the most comprehensive network testing tool that I've seen in a long time. Basically it has the philosophy of trying nearly everything possible - it's not quick but does give you a very comprehensive view of someone's connection. There's even a standalone client (for browsers who hate Java) and generates nice little result pages that can be shared.

Amusingly, one of my friends used to work for ICSI. They've got a cute little office.

They're doing excellent stuff. :)