NutCase Gzip for Mac

From Black Diamond Products:

The easiest way to start NutCase Gzip is to drop one or more files onto the program icon. Or you can fire it up by double-clicking the program as normal, and then drop one or more files onto the program window from the Finder, or open a file in the normal way from the menu.

NutCase Gzip automatically determines if the file is a Gzip file or not, and unpacks or packs accordingly. Output is created in the same folder as the source file if possible, else in the program folder.