@@@

The @@@ file extension is related to the Microsoft CodeView and used for its screen files.

Screen files used in the installation and instruction by e.g. Microsoft CodeView for C. CodeView was a standalone debugger created by David Norris at Microsoft in 1985 as part of its development toolset.

It originally shipped with Microsoft C 4.0 and later. It also shipped with Visual Basic for MS-DOS, Microsoft Basic PDS, and a number of other Microsoft language products. It was one of the first debuggers on the MS-DOS platform that was full-screen oriented, rather than line oriented (like its predecessors DEBUG.COM and symdeb).