Occasionally you see mac files wrapped in a zip file b/c it's the safest way of transporting it across a windows network. But zip is fundamentally a windows format equivalent to SIT. And yes, exe is explicitly only windows compatible. You can unzip a zip file using StuffIt Expander. You can zip a file using stuffit deluxe or DropZip or whatever. On os 9 there's also another.

BTW zip files intended for mac will be specifically named '... for mac' or OSX!