ASP.NET Ajax Server/Client Source Code Released
In case you don't monitor Scott Guthrie's blog (which you should with his RSS Feed), he just announced the availability of source code for the ASP.NET Ajax Library. Both server and client side code. The Server is released with an Ms-RL license and the Client with an Ms-PL license.
The best part for me, are the PDB symbols. This will allow you to step into the code while in debug mode to walk around the code, and see what's going on, all without having the actual code installed on your machine.
Link : ASP.NET AJAX 1.0 Source Code Released