A brush file extension is related to the Xerox Doodle Brush bitmap image format.
BRUSH file extension - Xerox Doodle Brush bitmap image
What is brush file? How to open brush files?
File type specification:
The brush file extension is associated with the Doodle, a paint program for the Xerox Dandelion computer (related to the Xerox Star).
Doodle was written by Dan Silva (who later created Deluxe Paint) and Bill Bowman around 1980.
This brush 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.