I started writing a chess game where rather than just two players there are two teams of an arbitrary number of players each who vote on what move to play next. Pitting yourself against a crowd of 100 other players should prove entertaining.

Fun tech too.. using chess.js (https://github.com/jhlywa/chess.js/blob/master/README.md), chessboard.js (chessboardjs.com) and Firebase.com at the moment.