ATOM for Mac is ATOM in its own Mac window, with the whole app inside it so it opens with no internet.
GET IT: atominterstate.app/mac (Download for Mac). Tour managers and admins also find it in a browser on a Mac under the gear (Settings) > Resources > Get ATOM for Mac. macOS 12 or later, Apple Silicon and Intel Macs. Drag ATOM onto Applications, open it and sign in with your ATOM login once with signal so it can download your tour.
IT KEEPS UP WITH THE WEBSITE: every change to ATOM's screens reaches the Mac app on its own, the same way the iPhone app gets them. It downloads the new screens in the background, checks they really came from ATOM, and switches over when you come back to the window after five minutes or more away (with nothing unsaved), the next time you open it, or when you press Cmd+R. No signal: it keeps using the last version it had.
RESTART TO UPDATE: once in a while the Mac app itself gets new parts. Then a slim bar says a new version is ready; click Restart to update.
ALSO: Touch ID (or your Mac password) before Money opens, exports and PDFs open in their Mac app, printing uses the Mac print window, and the Go menu has Home, Tour Book, Money and Contacts on Cmd+1 to 4. Working offline works the same as on the web and phone.