We have many geographically dispersed members, we have this forum, and I found this handy PBEM FAQ:
http://www.rpglibrary.org/articles/faqs/pbem.php
How about it? We could have two or three DMs, so that the game doesn't hinge on one person being available to read tons of stuff and post frequently. There could be many players. The plots would have to be relatively short and simple, since they will be drawn out by the delays between posting, but we could have many things happening simultaneously (like in a LARP). It would probably be best to have a very light system, approaching the simplicity of LARP mechanics.
* Would you be interested in DMing?
* Would you be interested in playing?
* If you're interested, what kind of setting would you prefer? Give three suggestions in decreasing order of preference.
EDIT:
My vague ideas about timing and other mechanics:
* Maximum of one "meaningful" post a day. By "meaningful" I mean a player's statement of intent (I attack the orc, trying to disarm him with my sword) which requires a meaningful GM response.
* This does not apply to witty in-character banter between players who happen to be online at the same time.
* It also doesn't apply to asking the GM simple questions, asking for clarification, etc., as long as they're minor issues. They'd probably go in a different place, anyway.
* Until the DM replies, you can edit your Meaningful post if you've changed your mind about how you want to do something (perhaps as a result of witty banter).
* All posts are readable by everyone, so it's up to posting and reading players to separate player and character knowledge in their posts and in their heads. If something really needs to be secret, maybe we could allow emailing the DMs -- but only one secret action would be allowed per day (in addition to your public action).
* Participation on weekends should not be complusory, so maybe Friday + weekend should be treated as one day.
* You should check back and respond to the DM at least once a day. If you're involved in a scene with lots of people, and you go AWOL, the DM can decide your character's action for the day based on what you were doing before.