Nitris runs as a Java desktop application (Linux, Mac, Windows) and as an Android app (with some modifications also as an HTML5 web app or an iOS app). You can find it in our Git repository.
Game concepts cannot be copyrighted. However, The Tetris Company will harass or sue developers who use the Tetris concept commercially. Feel free to play around with the Nitris code or to use it as a starting point to roll your own. (Note that the code does not necessarily reflect best practices. The game emerged while I was experimenting with the features of libGDX.)