Platforms, demo & where to play
Windows PC is the current focus; start with the official Steam page.
PC and demo
Steam offers the Moonfrost demo. The official FAQ also mentions Epic Games Store plans, while the October launch announcement specifically names Steam.
Mac, consoles and mobile
Mac is not the current development focus. The FAQ says there are no mobile plans. The sources checked here do not confirm a console launch.
Before starting
Check the requirements and save-transfer pages, especially if you played an earlier demo.