Just for those who might be interested, what you're describing is basically what's been going on over at
Shadowland Six for the better part of, oh, twenty years.
It's a bulletin board system set up with a file tree that breaks down IC and OOC pages in folders, with folders for various parts of The Sixth World (we've occasionally had continent hopping), so that one might open a series of folders to reach a specific page/location, where you make posts with HTML (not unlike making a basic post here). We've got built in die rollers, and even secondary/tertiary systems set up to handle alternate die rolls -- World of Darkness stuff, D&D, you name it.
For given bar, for instance, you might find yourself accessing Shadowrun->The Sixth World (IC RPing)->Seattle Metroplex->Puyallup->The Hollow Point. The owner of the Hollow Point may have two to three pages set up, one for role playing on the street outside, one for role playing inside the bar proper, and one set up for OOC stuff, like asking questions, rolling dice, or what-have-you. I say "may" when I should say "does," since the Hollow Point's actually a bar I created a long time ago over there. You create a page through Shadowland's interface, set up a description -- sometimes complete with images, sometimes only with text -- and you open it up to let people post there. Characters come and go, interact with each other, and all that jazz all through HTML posts (sometimes with necessary die rolls).
There's a separate section set up specifically for more organized, less "sandbox," style play, where would-be GMs can assemble a group of players created with specific rules and guidelines in mind...but then those private campaigns can be run within their own separate folders
or, more popularly, can spill over into the general The Sixth World area (but just have a little more guidance). Your street sam, who's just killing time and getting a cup of coffee in between jobs, could suddenly spot a Meet happening in the corner, be embroiled in a go-gang fight being GMed by someone running an Ancients campaign...or could just bump into another 'runner, chat about the Ares job last month, and go about his day.
We've also got a separate set of sub-folders set up for handling Matrix runs -- so you can be a decker running through ice, or just a poster on the Shadowland BBS looking for work -- in order to keep the meat world and Matrix from tumbling together
too much. That's mostly for the SR3 games that were traditionally much more common, but it's worth pointing out that you can just be posting to a message board, totally in character.
We've also got a general chatroom (in its own pop-up window, so it's accessible while perusing pages and navigating the menu), as well as the capability for private chatrooms to be created, complete with die rollers built in. For a faster paced game, or the rare instance where you might be able to get several members of a group together on-line at the same time, folks can coordinate and roll in the private chat, just taking the time to hammer out a paragraph of HTML and click the "post" button in order to show the action on an IC page.
Now, a caveat; the place is dead right now, for the most part, and has been for some time. I mean, dead like disco. Maybe two, three, people still visit with any regularity. Lots of regulars jumped ship, lots of folks grew up and got real jobs (several of us as freelance game writers, for instance) or went to school and got busier (or graduated and got even busier), and blah blah blah, it's pretty slow going right now. On the bright side, that means it's an empty playground. Anyone that wanted to could create anything they wanted to, and have a blast without there being any toes to step on.
A resurgence of folks looking to do this sort of thing, though -- like the people showing an interest right here -- could be just the jump-start SL needs,
and y'all could benefit from having...well...the perfect on-line set up for what you're describing, since it's what SL was made for.
We've traditionally played SR3 over there, but there's plenty of SR4 that we tried to get started, too. Either edition would be welcome, and to be honest more SR4 players would be a good thing. New blood, and all that, to help make our "edition swap" more official -- there are so few holdovers to SR3 left, even on SL, that it might as well officially be an SR4 board.