Snowball - The Blog

From the site:

Web.UI for ASP.NET AJAX is deeply integrated into the AJAX Library client-side type system:

All controls inherit from the Sys.UI.Control client-side base class;
All controls implement AJAX Library type descriptors, providing type information at runtime;
The namespace and all types are registered with the AJAX Library type system;

Web.UI for ASP.NET AJAX exposes comprehensive client-side APIs:

An industry first, the same level of programmatic control is available on the client as on the server;
The new APIs fully comply with the AJAX Library client-side syntax and semantics;
State of the art client-side API reference documentation is included with the product;

Web.UI for ASP.NET AJAX is optimized to work with the ASP.NET AJAX UpdatePanel control:

All client-side programmatic changes are persisted to the server upon callbacks or postbacks;
Proper client-side dispose mechanisms are used to optimize browser's memory consumption;
Control footprint is highly optimized in order to provide the fastest callback response time.

More here: http://atlas.componentart.com/