UpRightDown is a project that creates multiple versions of the same basic plot scenario. The first issue was pretty simple; this issue, though, there’s a multi-stage episodic plot that contributors can present as narrative, song, video, photo montage, game, or pretty much anything else. There are also prizes this time around for the best plot contribution ($300) and best performance of a plot episode ($1000).
Sound a bit complex? They do a more thorough job of explaining. But I know from experience that they’re open to IF implementations of plot ideas.