Courts have found in the past that copying a game design closely enough is a violation of copyright (http://itlaw.wikia.com/wiki/Atari_v._North_American_Philips

Courts have found in the past that copying a game design closely enough is a violation of copyright (http://itlaw.wikia.com/wiki/Atari_v._North_American_Philips http://itlaw.wikia.com/wiki/Atari_v._North_American_Philips) and they've also found the opposite (http://itlaw.wikia.com/wiki/Data_East_USA_v._EPYX http://itlaw.wikia.com/wiki/Data_East_USA_v._EPYX). Also see this discussion on misc.misc, circa 1990, re: the Lotus 123 spreadsheet wars: If the plaintiff cannot show that the target customer audience is UNlikely to recognize that the defendant's product is not the same as the plaintiff's then recovery is barred. Mere similarity between plaintiff's and defendant's products is not sufficient to support a successful lawsuit. Zynga may have a case here if they can prove that there was intent to make users think these were Zynga's games. (i am not a lawyer, i just cut-and-paste from USENET)