The "C# WebServer" is an open source, web/application server that runs on both DotNet and NovellMono. It is packaged as a library so that through a series of calls, you can set up various components such as an HttpListener, sessions, file serving, redirect rules, etc. It's very modular.
You can get the latest source code with:
svn co https://webserver.svn.codeplex.com/svn/trunk HttpServerTrunk cd HttpServerTrunk cd HttpServer msbuild dir bin\Debug
See also: WebDevelopment