.$$f is OS/2 database
Key Features: .$$F File Extension
What is an .$$F file?
The $$f file extension is related to the OS/2, an operating system with graphical user interface for IBM-PC compatible computers, developed by IBM.
The $$f file contains database from OS/2.
This $$f 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.