Look, we all go way back and I owe you, from the thing with the guy in the place, and I'll never forget it. - Reuben, Ocean's ElevenMy approach to creating and running a sandbox means putting lots of balls in the air at once. I've used the traditional dungeon and megadungeon as analogs for the social relationships, factions, and intrigues which provide the focal point for action in my campaign, and like a vast labyrinth of corridors, rooms, tunnels, and caverns, the intricacy of those complex relationships et al. becomes apparent the more the adventurers explore. Keeping it all straight requires some real effort on my side of the screen.
So, what about the players?
In a dungeon crawl, the players and their characters are likely working from an actual map, created as they explore; it is more-or-less - hopefully more! - a representation of what the referee sees on his side of the screen. Virtually every map I recall was covered with annotations, descriptions of monsters and traps and treasure left behind, names of characters, records of battles lost and won. The map which we produced in play was our record not only of the physical space but of events and interactions as well. But our campaign doesn't generate a physical location map of the sort with which dungeon explorers are accustomed, so that's meant looking for other ways to keep them up to speed.
First, our adventure logs provide a record of the events of the game. The wiki format allows me to link to the pages of characters the adventurers meet and locations they visit, immediately cross-referencing 'the guy' and 'the place' with 'the thing.' We've referenced the logs a few times during play, when memories around the table proved hazy. The adventure logs are composed from the notes I keep as we play, and they are checked by the players to make sure I didn't miss anything important to them.
I also use ability checks - roll under Wit on 1D20, usually - as a means of a determining something a character might know about the setting, or to recall a detail that the player is struggling to remember. The characters in my campaign aren't explorers in a post-apocalyptic wasteland - much is known and knowable to their characters without the need for first-hand discovery, so giving the players a roll to determined if their character knows a fact, based on background, skills, or career, is a reasonable way to represent the depth and breadth of their of their characters' experience.
Finally, I tried to build a relationship map for all of the non-player characters of the game-world, but neither writing it out by hand nor using any of the different software programs at my disposal was feasible - there are simply too many relationships for me to manage graphically, and it's not really all that helpful compared to the other options that the wiki provides for managing the many connections between characters. A relationship map is, on the other hand, perfectly feasible to produce specifically for the player characters, to diagram the relationships which they've created in the course of their adventures. I'm using Dia to produce this relationship map. The first draft simply shows the people with whom they've interacted so far, but I'm working on a second draft which includes organisations and places as well, which is proving a bit more of a challenge to create visually than I'd hoped - when it's done, I hope to be able to present them with a 'map' of the 'social dungeon' they've been exploring.