UNSTUFF (ver 1.1) Abandoned Freeware UNSTUFF is a program that can decompress the contents of StuffIt archives including archives created with StuffIt 1.5.1 through StuffIt Deluxe 3.0.3. Items which have been encrypted or optimized (with a StuffIt compression optimizer) cannot be unstuffed by this version of UNSTUFF. A StuffIt archive is a (Macintosh) file that contains one or more compressed files and directories. Most StuffIt archives have the ".sit" extension.