There is only one file type that uses the .MONTAGE extension:
Montage Screenplay File
Screenplay script created by Montage, a screenwriting application for Mac; contains the movie script as well as information for scenes, characters, and locations; also stores information for the screenplay publishing process, such as research, tasks, contacts, and queries.
MONTAGE files are used for creating well-formatted movie scripts, as well as for managing the screenplay advertising process.
NOTE: Mariner Software discontinued the development of Montage.
Updated: November 22, 2020