This excellent DLC for M&B Warband is on sale on steam for 2€. If you don't have Warband you can pick it up for 4€.
Why is it excellent? It's a mutliplayer only mod but if you join a clan you can participate in huge line battles with 200 players. It's essentially Empire Total War in Third-Person or like the Battlegrounds mod for the Half-life games in much larger scale (with better melee). The melee system differs a bit from Warband, it's easy to use but difficult to master. It's a very interesting skill-based system.
The Clan I'm in is called 77y, if you buy Napoleonic Wars you should check it out. All you need to do is write a short application to join.
http://77yregiment.com/But it's not just line battles, the game also has huge siege battles. As demonstrated in this video:
http://www.youtube.com/watch?v=Bljvu9447yYSiege battles are even more fun.
