I was playing Rimworld while visiting my parents over the holidays on their mac but I couldn't find the save game files to bring home with me.
- The file ReadMe_SaveFiles.txt in the root of the package says they should be in a folder in Users/[username]/Library/Caches/... but couldn't find a rimworld-related folder there.
- Google led me to a post on reddit (http://www.reddit.com/r/RimWorld/comments/2js9gu/for_mac_users_upgrading_to_yosemite_could_cost/) saying that it was a unity bug and that they should be in .../Library/Application Support/... There was a folder there (named something like unity.ludeon.rimworld) but it was empty.
- The "Open save data folder" button in the settings screen did nothing (note: I had a bunch of mods installed at the time, so ignore this point if no one can reproduce).
Unfortunately, I am home now and cannot reproduce any of these problems on my Windows computer (even with the same mods installed) and my parents aren't computer-literate enough for me to get them to hunt for the files. As for my colony, I can only presume that there has been a catastrophic failure of the underground geothermal generator and they have all been boiled alive in their sleep without having a chance to call for help :).
For windows its C:\Users\username\AppData\LocalLow\Ludeon Studios\RimWorld\Saves
What you could try is using finder to search for RimWorld or Ludeon Studios
oh...ummm
http://www.reddit.com/r/RimWorld/comments/2js9gu/for_mac_users_upgrading_to_yosemite_could_cost/