I have previously ran a 3rd ed game for a bit where the players were working for an inter planar agency called the society, they were based on a prime world where the society had a Mansion and trained teams (consisting of races from across the planes) on various digs and sites around the country of Leone (a kinda cultured Italian/french type country)
The players explored and dug about a bit finding out about one of the characters father who has a flying ship, and about a mysterious room within a mine with magically locked doors. Eventually a massive dragon army assaulted the fortress near the mine and the characters got plane shifted off by a high ranking member of the society, ending up in Sigil.
So now our current 4th ed game will be stopping for 3 weeks while the DM writes up some changes to the official module to make it to his liking, I've offered to run a one shot where the players will be playing a group of reclaimers who work for one of the players contacts within Sigil (an old goblin wheeler dealer named Spider) and they'll get to [sblock=not for shabe

] go back to the original prime world to possibly loot over the society's mansion and the Kings 2 castles. [/sblock]
I'm doing this as more of an exercise to see what I can do with 4th ed as it is I've just asked for fighting styles, race, personalties and maybe a role they see themselves fitting in, not written backgrounds, not character classes, not this or that magic item.
I aim to write up powers and items for each character based on what the players tell me about the concept rather than letting them pick so we'll see how it goes, I expect it to be a lot of fun but we'll see.
One concept back already a Kobold were-weasel
EDIT: Cheers black rat