Am I free to sell my game when I've finished?

Absolutely, there is an option in the FILE menu called Save Standalone which creates a new game folder with your game executable and all the required files, most of them encrypted to protect your custom art.  You can package these files any way you wish and distribute or sell them as you see fit. You can also entirely change the initial splash screen which is included with the standalone to hide the fact it was written in GameGuru. No accreditation is required by us when you export your game. You created the game, you should have the right to sell it without worrying about licenses and royalty fees.