Instructions for Mac users.
First decide where you will put your additional copy of TrippleA, ideally with a version specific name. I put mine in the Applications folder under my user home directory like this:/Users/simonhibbs/Applications/TrippleA_27_15256
Download the DMG file from the release in GitHub as above.Go to your downloads directory and find the dmg file, something like this:
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Double-click the dmg file and it will open a folder view. This is because dmg files are disk images so it treats it like a drive or folder:8dac1698-eca2-4859-8fbd-b256f36ff6d7-image.png
Do not run this. Click-hold and drag the TrippleA.app file from the dmg window into the directory you prepared in step 1.
You can now run this copy of TripleA by just double-clicking on the .app file in the folder. The first time this will probably be blocked by the OS. If so, open System Settings and go to Privacy & Security, and you should see a warning like this below. Click on Open Anyway, but only do this if you understands what you are doing and where you got the file from. Please use your own discretion.
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NOTE: This separate version of the game will use the same Engine Settings as any other version on your Mac. This means it will use the same downloadedMaps directory and savedGames folder.