From www.asp.net:
"The first public Beta release of Microsoft ASP.NET AJAX v1.0 (code-named “Atlas”) is now available for download. ASP.NET AJAX is a free framework for creating client-centric, interactive Web applications that work across many popular browsers and on any server platform. This Beta release is a preview of the fully-supported version of ASP.NET AJAX scheduled for release by the end of this year."
For those who haven't been following the development of this library by Microsoft, it was previously named "Atlas" and only recent changed to ASP.NET AJAX. There has always been the notion of two separate parts, the client library and the server library. The client library is pure javascript and can be used with most browsers, while the server library is for use with ASP.NET Web Applications.
With the release of v1.0 beta, the server library now comes in two separate installers. One is for the core ASP.NET 2.0 AJAX Extensions and the other, ASP.NET AJAX CTP, provides features that are still under development. Go to the Ajax.asp.net download page for more details on the available downloads.
Note that new documentation and a new version of the ASP.NET AJAX Toolkit was also released as part of this update.
For more infomation, go to the source: http://ajax.asp.net