OpenUp allows you to double-click on compressed and archived files and have them open in the Workspace. It supports decompressing PAX, GNUTAR and ZIP archives, as well as arc, arj, atob, uuencode, bzip, toast, gzip, compress, lha, pax, zip and zoo. More formats than Stuffit Expander.
MacOS X 10.0 or later
*Previously available here