XSP is a simple, standalone web server written in C# that hosts ASP.NET's System for Linux[1] and other Unixoperating systems. It runs on the Mono runtime for Linux and the .NET Framework runtime, making it usable as a lightweight web server on any platform supporting .NET.[2]
XSP was the original name of the internal project at Microsoft that became ASP.NET. The name pays homage to the original name of what became ASP.NET.