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I recently purchased (for $0) Hack! Firearms. I found nothing interesting about it so I decided to write up my own rules. Guns is a (barely) one-page ruleset for guns that foregoes boring historical accuracy. Inspired by AD&D 2e gun rules.
Next is something that was inspired by posts at Necropraxis and Maziran's Garden about segueing into strangeness from a traditional OSR setting. So here's Sanctuary, a demi-plane made by an insane wizard to preserve cultures and train adventuer-explorers. If you need help filling in villages Raging Swan's GM's Monthly Miscellany has some free village sketches. Training dungeons can just be plopped down; for example, dungeon 1 could be Golden Eye of the Kobold King (spawns 2d4 kobolds), dungeon 2 could be B4 The Lost City (or just the top four levels; spawns 1d4+1 hobgoblins), dungeon 3 could be The Hyqueous Vaults (spawns 1d6 eel-men), etc. For portals you have to decide if all three lead to the same world/plane or different ones. For example, all three could lead to Athas (the world of Dark Sun) then north/blue could lead to Tyr, yellow/west could lead to Nibenay, and red/south could lead to The Last Sea. Or one could lead to Athas, another could lead to another setting, and the third could lead to a 3rd setting.