Sally Forth Miniatures offers a free set of rules for playing solo Science Fiction miniatures games. While designed for ACP164, they are adaptable to any sci-fi miniatures system, such as WH40K, Void, Star Wars, etc.
Rules: Science Fiction
Big Game Hunt Dinosaur Hunting Rules
Big Game Hunt is a game of dinosaur hunting. Really.
Fallout Warfare
Fallout Warfare is a set of miniatures rules for playing games set in the universe of the acclaimed Fallout computer game.
Nuclear Renaissance Rules
Ramshackle Games offers Nuclear Renaissance, a set of free, downloadable rules for playing skirmishes set in a post nuclear holocaust. There’s both a full color, and a printer friendly set.
The game puts me in mind of one of the favorites from my childhood — Gamma World. You had to love that chart for checking out various objects you discovered.
Minimal Space Combat
Minimal Space Combat is a set of free wargames rules designed to give players an introduction to wargaming and space games.