Yes, GPL.

At the time I had seen that it had been forked into numerous private repositories, I believe roughly 100 or so. Perhaps I could have made a claim to have the other app taken down through Google Play, but I had no faith that this would be resolved, and even if it would be, it would be an ongoing problem.

As for whether they would have made open source contributions or not is in the end a moot point for me, because the only change that I observed was that they changed the colors and typeface and extracted the in-game menu into a separate welcome screen. I would not have merged this back into my repository.

While I myself violated the copyleft of my project by taking it closed source, I felt that it was my only resort. I've continued to develop the game over the past few years and by modernizing it and adding additional content, I've been able to significantly outpace my competitor.

For me, this ordeal had been a bit of an eye opener. I came out of university fully supportive of open source and when I discovered how this affected a real world project, I genuinely approached this situation understanding that it was just a risk I needed to accept. However, in the three years that it was available on GitHub, I received only two small PRs, and combined with the license violations, I felt that there was really no advantage to keeping it open source.

While this is just my anecdote, it has changed my perspective on how open source can realistically work more broadly. I honestly can't envision any kind of business that needs to offset large production costs able to publish that content viably as open source.