A framework which comes with prepared scenes and classes to kickstart your card game, as well as a powerful scripting engine to use to provide full rules enforcement.
Actually the demo is setup to have use custom/CGFMain.tcsn which is inheriting core/Main.tscn. CGFMain has board_scene set to CGFBoard.tcsn. This is the way it should be setup for games anyway.
If someone doesn't read the quick start the demo should still work. Setting defaults will prevent crashing if they just run the framework.