Call me crazy because I don't actually think using this proposed software would be all that much fun, but it might make for an interesting RoR project. Here's the idea:

A person creates a project (it has some intro text and all that malarky) and invites people to join it. Each person who joins will participate. A moderator (not necessarily the owner) will arrange all the participants in an order. After a person makes a post an email will be sent to the next person in line. They will then have x number of (units of time) to accept or decline their turn. If they accept they have a deadline. Should they decline or pass either deadline the turn will progress down the list. This will continue until such time as the project creator determines the project is "done" and "closes" it.

I'm sure I've seen of sites doing something like this, but this would be free-form, not a GM-led anything, and more of a turn based campfire story. You wouldn't play a role, you wouldn't just write one character, when it's your turn it's your story, write as much as you want. Sort of like "Once Upon a Time" without the cards or the interruption rules.

What do you think?