When you first launch the demo of this game, it presents you with a lengthy EULA. Presumably, that EULA grants BigFish Games permission to download and install GameManager.app in the Applications folder, because that's what it proceeds to do when you click 'Agree', in a process that can only be interrupted by force quitting the application. After it finished installing GameManager.app, it launches the game, but it then requires you to provide your email address before you can play. That's the point at which I quit and deleted the game. To fully remove GameManger.app, delete the following:
~/Library/Saved Application State/com.bigfishgames.*
A free alternative to this game is Coblyn.