Will Grasshopper work on the Mac?

It does exist...

A very early version of Grasshopper for Mac is available in the RhinoWIP for testing and feedback.

Users of Rhino 5 for Mac have access to the RhinoWIP.  

The most recent version of the RhinoWIP contains a command called "ExplicitHistory".

Please post feedback and report bugs (there are many!) on the Grasshopper for Mac category on Discourse.