The ASP.NET AJAX Control Toolkit is a classic set of ASP.NET WebForms extensions that helps you build ASN.NET websites. Now maintained by devexpress.com

Bootstrap MVC provides additional methods for the MVC HTML Helper in order to generate HTML Code for the Bootstrap framework.

This a simple tool for Application and Web page designers. Color combiner can be used in choosing best combination of colors

DiffPlex is a combination of a .NET Diffing Library with both a Silverlight and HTML diff viewer.

The Halide C# API is a set of classes that will aid the ASP.NET web developer in creating rich web applications, with less work.

This is an HTML parser that builds a read/write DOM from “real world” HTML files. It supports XPATH or XSLT and is tolerant with "real world" malformed HTML.

This is an HTML Application Host framework for building HTML5/regular HTML/JavaScript for Windows Phone. The framework consists of controls needed to support embed html apps in a standard xap format used by the market place for deploying to windows phone.

HTMLWriter is a utility library for generating html fragments or documents based on the StringBuilder class. It is intended for generating raw html text that could be used for reporting or displaying inside a WebBrowser control (in Winforms or WPF).

The nWeb Data Extractor Library provides support for extracting data from the http response html, it allows user to convert http response HTML to XML, then allows user to extract desired data form the generated xml file.