David Medlock offers The General Purpose Wargame, a set of semi-skirmish level wargames rules for simulating battles from the Stone Age to the Victorian.
Miniatures Rules
Gut Check Solo 15mm Science Fiction Rules v1.7
Gut Check is a set of free wargames rules for 15mm science fiction battles. What makes it unique, I think, is that it’s designed from the start for solo play. The author lists its features:
Designed from the ground up for solo play
Fast playing and zero bookkeeping
Uses normal 6 sided dice (Usually rolled no more than 2 at a time)
Uses activation rolls modified by battlefield conditions for turn sequence
Seamless Over watch and suppression effects built into system
Use any miniatures
Played on a Hex grid for convenience, but could be played with little fuss on a standard table
Foundry Street Violence Rules
Some years ago, Wargames Foundry published a set of rules to go with their Street Violence figures. They’re missing — as far as I can tell — from the Foundry site, but you still can get them as a free download at The Warstore.
Dungeon Delvers Rules
Dungeon Delvers is a set of free dungeon crawl rules.
Renaissance Naval Rules
David Heading offers a set of free wargames rules for Renaissance Naval Battles.