1. Download the game and navigate inside the folder to find Game.app
2. Choose "Get Info" from the context menu and scroll down to the Sharing and Permissions part.
3. Check that your active user (marked with (me) after the username) has Read and Write permission.
4. If it's not the case - set it yourself via the menu. After changing permissions click on the gear icon and choose the "Apply to enclosed items" option from the drop-down menu.
5. Now we are sure that your access rights are adequate and you are ready to add the game to your applications. Do so by drag-and-droping the Game.app into your Applications directory (by default it’s displayed on the left side of the Finder.) This will require Administrator access.
6. Run the game and get inside the options right from the main menu. The first time you execute it MacOS will warn you that I am not a licensed Mac developer. Oh noes. Ignore it.
7. Change something like a volume level in option menu and hit escape to check if the error appeared on the screen.
8. Start a new game and try to save your progress. Check if you can save the game and load afterward.
9. Great! Now you can be sure everything runs smoothly.
If you can't launch the game by just clicking the game.app icon try to open the content folder and use the NWJS terminal icon within the MacOS folder.