Most Irregular is horse and musket rules extension to the Fast and Dirty skirmish rules, found on the same page.
Rules: Napoleonics
Paintingshed Napoleonic Rules
Steve Jones offers his Paintingshed Napoleonic Rules. The rules are written for 6mm figures.
A Fistful of TOWS: 2000 Modern Miniatures Rules
Here’s the latest version of A Fistful of TOWS, Ty Beard and David Burnett’s classic set of modern armor rules.
Quick Rules For Napoleonic Skirmish Games
Jackson Gamers offer a set of quick rules for Napoleonic Skirmish games.
Austerlitz To Waterloo Rules
Wes Rogers offers Austerlitz To Waterloo, a set of free wargames rules for Napoleonic warfare. The rules are designed for 25mm – 30mm figures, where one figure equals 25 men.