If you set the in-game Option for fullscreen on the Mac OSX version, then at the next launch the game will crash with a segfault.
Using the green 'fullscreen' button at the top-right of the window to use fullscreen does not set this option in Narrowboat Simulator's user data, so will not cause this crash.
For a swift fix, I suggest (for the Mac version alone) removing the in-game fullscreen option.
(If you encounter this problem, you will have to edit ~/.godot/app_userdata/Narrowboat\ Simulator/save_game.dat to remove the fullscreen setting.)
-- Giles.