Minden Rose is a set of free wargames rules for playing Seven Years War battles. It is designed for 25mm or 15mm figures.
Rules: Age of Reason
Richard Bradley’s Seven Years War Rules
Richard Bradley’s Seven Years War rules are designed for 15mm figures on a 40mm frontage.
The Square Brigadier Rules
The Square Brigadier is a set of horse-and-musket rules based on Bob Cordery’s Chess board game inspired by Joe Morschauser.
Argad Medieval Skirmish Rules
Argad is a set of free wargames rules for skirmishes in the dark ages and for pirates in the 17th and 18th centuries.
Horse and Musket DBA Variant
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.