ASP.NET AJAX

ASP.NET AJAX is a free framework for quickly creating a new generation of more efficient, more interactive and highly-personalized Web experiences that work across all the most popular browsers.
http://atlas.asp.net

With ASP.NET AJAX, one can:
1. Create next-generation interfaces with reusable AJAX components.
2. Enhance existing Web pages using powerful AJAX controls with support for all modern browsers.
3. Continue using Visual Studio 2005 to take your ASP.NET 2.0 sites to the next level.
4. Access remote services and data directly from the browser without writing a ton of complicated script.
5. Enjoy the benefits of a free framework with 24x7 technical support provided by Microsoft.