Microsoft released version 1.0 of their AJAX framework named ASP.NET AJAX (fka Atlas) to the web. You can read the official announcement on Scott Guthrie's blog at http://weblogs.asp.net/scottgu/archive/2007/01/23/asp-net-ajax-1-0-released.aspx. 

As Scott explains in his blog the actual code along with samples, documents, and videos can be downloaded from http://ajax.asp.net.