Lightweight (<200KB) framework running on top of the ASP.NET 2.0 HTTP pipeline (HttpHandler)
Controller-based for easy implementation of the MVC pattern
Flexible template-based rendering engine (using pure HTML files) with full C# expression parser, view components, custom controls, ...
URL routing engine for routing URL's to controller actions
Easy to use form and postback handling with integrated validation framework, without viewstate headaches
Ajax form validation. No more postbacks, even when performing complicated business rules validation
Very powerful integrated testing framework for running unit tests on your web pages. Instead of running custom unit tests, the testing framework simulates a web browser.
Easy mapping of parameters and other client data to typed method parameters and class members
Built-in Ajax support. JavaScript method stubs are generated by the framework. Just call your server-side .NET methods from client-side JavaScript as if you were running them on the server.
Integrated logging and profiling via plugins
Built for performance
Simple deployment
Runs in partial trust environments
Fully customizable with plugins for:

Logging
Profiling
Visitor tracking
Custom controls
View components
Custom form validations