Finding open code games without GNU license

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http://stackoverflow.com – I'm developing an Android application for a company, and they ask me to insert a known game but changing a little bit for doing it more related with the company. For example, if we wanted to use Tetris, I will have to modify its pieces with some others I would create. I've been searching and most of that open code games have GNU license, so I would have to share my code, and that's not our purpose. So do you know where can I find some open code games for modifying and not needed to show my code? One solution could be paying for it, but I don't know where to search. Thanks in advance. (HowTos)