on windows you unzip and then run trailmix.exe.

On Mac you might have to do some annoying workarounds to get it to run:

Note: For anyone playing on MacOS Catalina who is having trouble launching the game:

1.  run chmod -R +x "Trail Mix 1.5 Mac.app" in the terminal
2. right click on it and choose "open", it should give you dialogue with an option to launch the game.