Blender works on Mac.  It provides some decent Python scripts, as I recall, for mesh reduction.  Recent versions of Blender also include retopology tools, although I haven't tested them to see how effective they might be....

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.