A dmm file extension is related to the BYOND Dream Maker, a development tool. A dmm file stores map.
DMM file extension - BYOND Dream Maker map
What is dmm file? How to open dmm files?
File type specification:
The dmm file extension is associated with the BYOND Dream Maker, an integrated development environment, used to build networked multi-user worlds.
The dmm file contains map from BYOND Dream Maker.
This dmm file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.