Just updating this older thread for a newer entry into the RSAT-on-Mac space called OpenRSAT, and it's amazing, way, way better than anything else that came before: Mac native (no bloody Java or PowerShell needed), completely free and open-source, and works like a charm.
For macOS releases, download the "darwin" DMG, either "arm" for Apple Silicon/Mx machines, or "x64" for Intel machines.