The Haunted Dimensions site has paper models of three small crypts. The only downside of these is that the back of the crypts are defaced with site advertising. Still, there’s also a brick wall there that you can paste the crypts up against.
Stormed At With Shot and Shell is a set of free miniatures rules for playing games set in the Crimean War. They’re designed for 15mm figures.
Charge Yr Pikes is a set of free English Civil War miniatures rules. They use a card driven turn mechanism.
In N scale here are some free paper models of the tracks of Chicago’s famous “L”.
Labyrinth Lord is a free “throwback” style RPG.
I’m old school, so I’m going to give this a serious look.