I have searched and searched but I see no open framework for turn-based multiplayer games. I am reluctantly about to create one. I am writing this because, honestly, I am surprised nothing exists.
What would be in the framework? Well this is what I forecast creating, for simple games like Poker, Hearts, MahJong, Scrabble, Backgammon and Chess.
A) Script for defining “pieces” or units (with links to artwork)
B) A websockets package for pipelining between clients and server
C) Conventions/rules for communicating game/board state
D) Ditto for communicating state changes (moves)
E) API between UI code and local client game code
Items A, B, C and D, if well designed, can make it much easier to write a new game, say Bridge, without writing a custom Bridge game from scratch. Item E makes such a system more modular agains different UI mechanisms (canvas v. html5). It also might provide a natural hook for AI players.
Those are -er- hypothetical elements. I am just spitballing at this point. Anyway, if something has been done in this area, I would love to hear about it.