Copyrighting an app or other software has more to do with the appearance of the code than the appearance of the software. If chunks of the code are copied and you had access to the code, there is an inference of copyright infringement. If you get to the same result using code that clearly suggests you did not copy the code, there is no inference of copyright infringement.
The appearance of the game can have the same result. If, with all the other puzzle games out there, the average person looks at the appearance of your game and thinks it was copied from Quell (not exactly copied, but copied and modified), you could have a copyright issue with the appearance of the game. The fact you are discussing making a puzzle game similar to Quell instead of just discussing making a puzzle game and being aware there are many out there is a bit of a red flag. It is ok to make a puzzle game because you were inspired by Quell, but don't make a game that feels like a derivative of Quell.
Answered on Dec 23rd, 2013 at 8:44 AM