The Withings Scale is a pretty simple piece of hardware. Set it up on your wifi network, weigh yourself, and it instantly sends your weight to the Withings website.
Now, as Withings isn’t really taking and analyzing a ton of data, it’s (apparently) fairly trivial to pull all the needed data from their website. However, there are those who aren’t completely happy with that solution, and who also don’t want to deal with the slow flash interface.
The people at Proxilium decided to reverse engineer the network protocol, doing a full trace on the communications between the scale and the home website, and extracted all of the data the scale sends to the website. Not only that, he shows how to set up alternate DNS rules to route off calls to the website to a local webserver, so you can have your own data store. Neat!