Forget Greyhawk. Forget Blackmoor. Way before the Forgotten realms, the original campaign world boxed set was Outdoor Survival by Avalon Hill.
I'd wondered for years about this boardgame mentioned in Men & Magic on page 5 as part of the Recommended Equipment to play the game. I stumbled across a reasonably priced copy on eBay in surprisingly good condition and have enjoyed reading through it. My mind wondered back to the early 70's and how this boardgame could form the basis for wilderness adventuring in the developing D&D game of Gygax and Arneson. It is firmly rooted in the style of gameplay of its day. No elegant "universal mechanic", instead it is a collection of rules that work together.
For someone like Dave Arneson who was much more idea oriented than a strict rules guy, this must have really helped him out to lay some ground rules for adventuring in the wilderness. I can see how the system could easily work with Chainmail without too much tinkering.
I've been considering the idea of using it as a base map for a new Swords & Wizardry campaign and it struck me how wonderful it would be to scan the map in and use modern digital graphics to turn it into a fantasy game world.
Just imagine it: Lavivrus, realm of ancient sorcery and high adventure!