openSEAL is C# .NET libraries & frameworks that aid development of enterprise applications using best practices & design patterns like MVC & SOA. It provides architects & developers a base to rapidly implement flexible, secure n-tier solutions.
CAjax is a library for building AJAX style web applications, which consists of a javascript package for easy writing object-oriented AJAX logic in javascript, and a set of server-side packages dealing with unified communication details.
Ajax.NET is an implementation of the AJAX technology used by Google, Orkut, Flickr, ... for the .NET environment. Call server side methods as if they were on the clientside.