paradisebunny
Explorer
Just to add to system neutral adventures: there is the dark of hot springs island, a dark tropical island hexcrawl sandbox and the great collection of one page Trilemma adventures
Ravensrook is a great system-neutral city setting book. It very much calls to mind dangerous cities of fiction such as Sanctuary and Lankhmar. I've personally used it as a stand-in for the Free City of Greyhawk when I wanted a city with a slightly more grungy feel and also as a city "core" for the City League in Pelinore.
It doesn't appear to be legally available online, and the few physical copies I could find are far too expensive.I could swear that it was available as a pdf a few years back but I can't find it on drivethrurpg if that was the case.
This is a great book, but it is dense. But if you've ever wanted to create a fantasy setting where you weren't handwaving where all the crops were or what all the NPCs do when they're not waiting to be part of the PCs' story, this is it.The obvious choice for me is A Magical Mediaeval Society: Western Europe, which goes into great depth about how mediaeval society actually worked, with pointers on feudalism, inheritance, farming, the church and so on. Although nominally produced for 3rd Edition, the historical stuff is system-neutral and even the various tables for NPC distribution and the like could be easily adapted for a non-D&D game.