Mount and Musket Battalion is a multi-player total conversion that tries to accurately represent the time period around the end of the Napoleonic Wars (1812-1815). It has historical factions with accurate units and equipment, including different types of infantry, cavalry and even usable artillery.
Played it for an hour or so today and it's a lot like Battlegrounds 2 for HL2. Although I believe the gameplay is better in this.
There are a few servers on BG2 that play only line battles and stuff, which is very fun. Just hope that they have the same in MM.