A late-medieval mathematical board game, known as 'The Philosopher's Game'.
Here's wikipedia on the subject, and here's a more thorough look at the rules.
Currently, this implementation includes Rounds, Triangles, Squares and Pyramids. They can all move according to (a set of) the rules, but no captures are implemented and certainly no victories.
The app runs on ES6, whenever possible. I.e., I have been using as much ECMAScript6 as Node.js 5 allows. I'm using eslint with airbnb's config.