The freecellsave-ms file extension is used by the FreeCells game in Windows. It stores saved FreeCells game positions. The files allow you to continue games where you left off. They are saved to [user]\Saved Games\Microsoft Games\FreeCell\.
To open .freecellsave-ms files, use the Load Game option in FreeCells. There is likely no way to convert them to other formats.
You may get errors opening .freecellsave-ms files if FreeCells or required Windows components are not installed. Download and install FreeCells to associate .freecellsave-ms files with the game.
The file could also be infected with malware. Scan it with antivirus software, which may recommend deleting infected files.
If you have the right software installed and no infection, there may be another rare issue. In that case, you likely need assistance from technical support staff.
The .freecellsave-ms binary format saves the game state. It was developed by Microsoft for the FreeCells game included with Windows. The file extension helps Windows recognize and open the game save files in FreeCells.
Microsoft FreeCell