So you can play coop chess but doesn't support computer or online opponents. What this does support is multi-dimensional chess. Pretty rad if you ask me. There's lot's of room for improvement including aforementioned lack of support as well as support for UI elements like menus and replays. The exercise was simply a working chess engine in Java for object-oriented class design without formal knowledge of design patterns. Play with it and play as many dimensions*.
*There is a limit based on how many boards fit in the window. This is silly and instead requires pagination and a search input to transport to board infinite-1 in a jiff.