Hardtack is a set of regimental Civil War rules based on the excellent Stargrunt II rules. With a scale of 1 fire = 3-5 men, it’s intended for fighting one regiment v another, filling the space between Johnny Reb and Brother v Brother.
The Jackson Gamers have a page with everything you need to know to start gaming Civil War Ironclads
Here are a set of house rules for “fine tuning” Fire and Fury, the great American Civil War rules set.
I’m not sure I’m on board with all of these.
Honor and Glory is a set of rules for the American Civil War for games where the smallest tactical unit is a regiment, which is represented by four bases. It’s playable in nearly all figure scales. Originally available on the Yahoo Groups, I have archived the files there because Yahoo Groups is shutting down.
Sandpit Showdown is a set of free wargames rules for backyard battles with army men in the Wild West and Civil War.