Simon Tatham is a software engineer who created a collection of portable single-player puzzle games. Simon is better known in some circles as the author of PuTTY, but as a side project this one has been rather successful. With the help of others there are now around 40 puzzles, which run on Windows (desktop and Store), Linux, Mac OS X, Android and the Web. They are well worth a look.
Link: http://www.chiark.greenend.org.uk/~sgtatham/puzzles/
The puzzles are Open Source and written in C. The common code framework is rather low level, which rather limits the ability to implement new games or port existing ones to a games engine like Unity. The relevance to the Polygamo project is as working models: in principle it should be possible to re-implement all these games reasonably easily.