Update: Have a look at Ajax.NET Professional at http://www.ajaxpro.info/. The Web site of BorgWorX is not available any more.
The source code is now available at SediSys. You can download the source code of the Ajax.NET library with any SVN client (http://subversion.tigris.org/). Beside the official command-line client programm a comfortable Windows GUI client can be found at http://tortoisesvn.tigris.org/. For anonymous access use https://svn.borgworx.net/SVN/BorgWorX. You will find the Ajax.NET library in the folder /trunk/Web/Core/Ajax.
There is a Wiki available at http://www.borgworx.net/ where we will build a documentation for Ajax.NET.
If you have source code changes please send it me or Christian Hubinger (SediSys). We will merge the changes with the Ajax.NET source code.
Update: The forum is available at http://forum.borgworx.net/.