Steam Iron and Tin is a set of 15mm ACW naval rules that was distributed to people who attended the 1985 Origins Convention in Baltimore (I was at that convention!).
Rules: American Civil War
State of War ACW Skirmish Rules
Richard Bradley’s State of War ACW Skirmish Rules are available at the Tyneside Wargames Club site.
ACW Rules For River and Coastal Warfare
By Jeff Peach & Les Booth offer a set of free wargames rules for ACW River and Coastal Warfare
American Civil War Rules – MAWS
Here’s a set of club developed American Civil War rules.
Gettysburg At The Gallop
From Baccus Miniatures comes Gettysburg At The Gallop, a set of free wargames rules for the American Civil War in 6mm.