Alan Saunders offers Great Northern War, a set of free wargames rules that he describes as:
A heavily modified version of the Horse & Musket/Pike & Shot rules in Neil Thomas’s ‘One Hour Wargames’ specifically for use with the Great Northern War.
See The Elephant American Civil War Rules
See The Elephant is a set of free wargames rules for the American Civil War played on a chess-like grid.
Mighty Mean Fowt Fights ACW Rules
Mighty Mean Fowt Fights is a set of free wargames rules for American Civil War battle games played on a square grid.
Struggle Against Everything And Everybody
Alan Saunders offers Struggle Against Everything And Everybody, a set of free wargames rules for the Mexican Revolution of 1910 – 1920.
A Hotter Fire ACW Naval Rules
A Hotter Fire is a set of free wargames rules for naval combat between civil war ironclads.