Mono project offers .NET compatible set of tools, including among others a C# compiler and a Common Language Runtime. It runs on Linux, *BSD, Windows and other operating systems. From the article:
The FastCGI Mono Server was developed as part of the 2007 Google Summer of Code (http://code.google.com/soc/2007/) with the goal of increasing the availablity of ASP.NET and simplifying configuration. Requiring as little as zero command line options and supporting a large number of servers, the FastCGI Mono Server makes it simple to include ASP.NET on your server.
This documentation contains configuration instructions for serveral web servers on Linux, with plans to expand support to Windows and Macintosh in the future. Please take the time to read all the information below before configuring your server.
(Fig. 01: How does FastCGI mono server works?)