There is only one file type that uses the .MAHJONGTITANSSAVE-MS extension:
Mahjong Titans Saved Game
Saved game file created by Mahjong Titans, a mahjong solitaire game included with Windows Vista and Windows 7; saves the current state of the game so it can be continued at a later time.
When you save a game while closing Mahjong Titans, you will be prompted to resume the saved game the next time you open the program.
NOTE: Mahjong Titans was renamed as Mahjong and the MAHJONGTITANSSAVE-MS file is no longer used to save games.
Updated: February 24, 2017