.FSX File Extension
File TypeVisual F# Script File
What is an FSX file?
Script written in F# (pronounced "F Sharp"), a functional programming language formally introduced by Microsoft with Visual Studio 2010; can be run with the "F# Interactive" component of Visual Studio; used for scripting F# code instead of compiling it.
NOTE: F# Interactive mode can be started in Visual Studio by selecting a segment of F# code and pressing Alt-Enter. F# scripts also use the .FSSCRIPT extension.