(1) This absolute gem works with Leopard (10.5.6 as of this writing).

(2) Though zip and gzip supposedly use the same algorithm (Zempel something-or-other), using gzip GUI Tar consistently makes smaller files, with no apparent speed hit.

(3) Truly a time saver over having to open the Terminal to accomplish an alternative compression to zip; this works fast and slick.

(4) Recommendations for a future version (and ask for some money): (a) a Contextual Menu plugin that offers formats if not compression levels (b) compression levels (fast and bigger, slow and smaller, etc.), could be pre-set in Preferences.

This is a great example of a GUI "wrapper" that is clean, intuitive and in the grand Mac fashion "just works".