Homebrew.
My low fantasy urban crime MRQ campaign is based in a huge fantasy city in a setting largely of our own creation. I'm using the city maps for Ptolus, mining books like Shadowspawn's Guide to Sanctuary, MRQ Lankhmar, and the Pirate's Guide to Freeport for inspiration, the Godfather and Grand Theft Auto for tone, and any mechanics from MRQ books I can dig out (such as a few Gloranthan Gods, demons from Elric, etc.).
Unlike Lankhmar, magic is not corrupting and black in my campaign. That said, it's similar to most swords and sorcery worlds. It's very rare. Hardly anyone has ever witnessed magic, and those that do tend to be terrified of it. Those who have it tend to be secretive cults that horde their divinely imbued magic. Membership requires dedicating one's soul to their deity, and the cults for each deity have their own agendas...
As you can imagine, the lack of healing magic makes the game fairly bloody.
I don't expect the PCs to ever leave the city, nor to even care about what lies beyond the walls. They are far more wrapped up in protecting their turf, and fighting rival criminal syndicates in order to expand their territory, raising in status within the organization of cult of the God of Thieves, etc.