The Square Brigadier is a set of horse-and-musket rules based on Bob Cordery’s Chess board game inspired by Joe Morschauser.
Bar Brawling is a set of skirmish rules for wild west barroom brawls.
Black West is a simple set of free wargames rules for skirmishes in the Old West.
De Bellis Indica is a DBA variant for warfare in India in the 18th and 19th Centuries.
Here’s a Horse and Musket DBA Variant — primarily for Napoleonic and Seven Years War, but since the basic principles of war in that era covered a huge number of conflicts, you could adjust as needed.