See The Elephant is a set of free wargames rules for the American Civil War played on a chess-like grid.
Rules: American Civil War
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.
A Hotter Fire ACW Naval Rules
A Hotter Fire is a set of free wargames rules for naval combat between civil war ironclads.
American Civil War Campaign Rules
The DFW Grognards have published a set of ACW Campaign rules.
Give Them Cold Steel Civil War Rules
Give Them Cold Steel is a set of free wargames rules for the American Civil War.