FileInfo.com - The File Extensions Resource

.FS2 File Extension

File Type	FreeSpace 2 Saved Mission File
File Format	File
Common?	No
File Description	Game saved in FreeSpace 2, a space combat simulation game released in 1999; used to resume progress in a specific mission; can be opened in FreeSpace 2 or edited with FRED 2, the FreeSpace 2 editor.
Program(s) that open fs2 files	Windows: Interplay FreeSpace 2; Edit with FRED2

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/fs2