.! is Screensaver temporary data
Key Features: .! File Extension
What is an .! file?
The ! file extension is reported to have been used for some sort of screensaver file.
Perhaps temporary data generated when screensaver in Microsoft Windows or other operating systems is operational.
This ! 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.