The Free On-line Dictionary of Computing (30 December 2018):

Stuffit
sit

    (filename extension: .sit) A file
   archiving and compression utility, developed by Aladdin
   Systems, Inc..  Stuffit was originally developed for the
   Macintosh and is still the Mac standard tool for compression
   and archiving (compressing multiple files into one).  Stuffit
   is now also available for Microsoft Windows and Linux.
   Compared to the standard Windows tool, WinZip, it is faster
   and gives better compression.

   Stuffit archives can be extracted with Stuffit Expander.

   Stuffit Home (http://stuffit.com/).

   (2003-09-20)