At a glance
RimWorld has a Mac version: Steam sells it for macOS. The Mac requirements list only Intel: on Apple Silicon Rosetta 2 runs it, and old Mac versions sometimes do not start on current macOS. Try it in Steam for Mac first.
RimWorld came out on Steam on 17 October 2018, made by Ludeon Studios.
What your Mac needs
The Mac requirements list only Intel.
Minimum macOS in the Steam requirements: 10.12.
Steam requirements list at least 4 GB of memory for RimWorld.
Allow about 1 GB of disk space for the Mac version.
How to play
Open Steam for Mac and install RimWorld as usual.
If the Mac version will not start, you can install the Windows version through Uncork: download Uncork, sign in to Steam and install RimWorld from there (1 GB). We have not tested it ourselves.
The Windows version through Uncork needs a Mac with Apple Silicon (M1 or newer).