There is only one file type that uses the .MMC extension:
Microsoft Media Catalog
Contains a collection of images (such as a clipart gallery) or other media in an organized format; typically saved in the \Application Data\Microsoft\Media Catalog directory.
An example of an MMC file is the "Artgal50.mmc" catalog file, which contains images, keywords, and thumbnail previews used by Clip Gallery.
|Microsoft Clip Gallery|
Updated: February 7, 2008