Grinning Man Entertainment will be posting a free set of American Civil War rules called Then Holler.
From their announcement:
We’re just finishing up the basic work on “Then Holler,” a ruleset for roughly division level Civil War miniatures gaming. With no real idea as how to proceed from here, we’ve set up a website which we’ll use to publish designer’s notes, scenarios, orders of battle, and the full basic rules over the coming few weeks.
The website can be found here: www.grinningmanentertainment.blogspot.com
For the tl;dr folks: “Then Holler” replicates Civil War combat with an incredible amount of historical accuracy, a bare minimum of luck, and takes about ten minutes to learn.