Today I stumbled upon wikipedia articles about the livery companies of the City of London and the notion of "Freedom of the City".
It's very fun, almost Pratchettian, that they have a guild for everything. The Worshipful Company of Makers of Playing Cards? The Worshipful Company of Human Resource Professionals? You can't make these up.
I will confess that I have been pretty down on adventurers' guilds. Does it make sense to have enough wizards in a city to warrant a guild? Or for thieves to have an officially-sanctioned, chartered liveried company? Does it make sense to have a single guild for all of the adventurers, despite their divergent interests and the danger to stability that concentrating all that firepower into a single organization has? Maybe not (then again, maybe the thieves' guild just has a front company). But it is probably fun, particularly if you have a city government where guilds elect the Lord Mayor and your wizards' guild candidate is running against the haberdashers' guild's candidate (backed by the thieves' guild, perhaps). There's probably room for an amusing variation on ACKS' senate rules for guilds electing city leadership, if you're into that sort of thing.
The choice between guilds specific to a particular city vs cross-city guilds like the Hanseatic League is also an interesting one. An inter-city guild provides for players wherever they may happen to be, while a single-city guild without reciprocal privileges elsewhere ties players to a particular place; it creates a home base.
This home basing effect ties somewhat obviously to halls and refuges. Freedom of the city also ties nicely to some of the ideas from the halls post. Someone (or a military unit) granted freedom of the city can do things like carrying arms in the city.
There are a number of rights traditionally but apocryphally associated with freemen—the right to drive sheep and cattle over London Bridge; to a silken rope, if hanged; to carry a naked sword in public; or that if the City of London Police finds a freeman drunk and incapable, they will bundle him or her into a taxi and send them home rather than throw them into a cell.
Obviously a relevant and desirable status for adventurers! And one which a city council might be careful to grant! A good motivation for quests - "if we help Edmud the Haberdasher with his missing shipments, maybe we can secure his vote to get freedom of the city." Basically: citizenship, but of a particular city.
This provides a potential non-mechanical form of progression or campaign progress. As does progression from freeman to liveryman of a particular guild (with voting rights in city elections). And then across cities.
This idea of medieval cities with independent governments whose freemen are not tied to feudal lords is also an interesting deviation from ACKS' assumptions about the relation between cities and high-level fighters, where cities are largely subsidiary to a particular domain. An independent city council and Lord Mayor might come into conflict (open or otherwise) with adjacent feudal domains-holders.
