Matthew Hartley has a game called Kraken, inspired by the man against sea monster scene in Jules Verne’s 20,000 Leagues Beneath the Sea
rules
Event Horizon Starship Combat Rules
Event Horizon is a set of free wargames rules for quick play starship combat. It is played on a grid board.
The Devil’s Brigade WWII Rules
The Devil’s Brigade is a set of free wargames rules for WWII skirmishes.
Jungle Ashanti Wars Rules
Jungle is a set of free wargames rules for the Ashanti Wars.
Breaking of Nations Universal Rules
Breaking of Nations is a set of free wargames rules for 25mm skirmish actions. Originally meant to be for the first World War, the can be used in a variety of settings. There is also a colonial variant.