Anthem.NET is a free, cross-browser AJAX toolkit for the ASP.NET development environment that works with both ASP.NET 1.1 and 2.0.
Avoid this project. It's been dead since 2007, and at the moment doesn't work on Internet Explorer 8.
This is maybe the best Ajax .Net Framework ever. Fast, easy to implement, tiny Js Files... So, whats wrong to not recommend it? It's abandoned: no support, no bugfixes, no programmers answering questions, no updates, no .Net Framework 3.5 (and up) compatibility, no url friendly/Url Rewrite support and incompatibility with gZip/deflate server page compression. It's a pitty because it's a great project and I (and many others) love it but the fact that has not being updated since 2007 makes it useless for some modern applications. Please, come back, you are really talented. Please, continue this marvellous project. Thanks!