Maybe I'm tempted to do a play by post game because I'm using #4thewords (a game/app/thing that encourages you to type words every day), and I think play-by-post is an ideal case for that. In a play-by-post you should ideally respond to the stuff other people type quickly, and even if you're waiting on replies there's always more worldbuilding to do.
Anyone know any good play-by-post arenas or cooperative #worldbuilding projects that are popular in this present epoch?