The Armchair General offers a set of free wargames rules for 25mm / 28mm Napoleonics called A Marvelous Victory
Eagles and Emperors is a set of free wargames rules for the Napoleonic period based on a set of Civil War rules called The Blue, The Grey and the Butternut.
Bring Out The Old Guard and That Vertically Challenged Mediterranean Man is a set of free wargames rules for the Napoleonic period.
eRules is a set of free wargames rules for the Napoleonic era. From the introduction:
eRules Napoleonic.txt is a set of rules for the Napoleonic wars designed by WargameSystems following the same principles as eRules World War II, except that Napoleonic.txt is provided free as a draft document for you to download, try out and contribute to. Let us have your suggestions for adding to it or improving it.
La Bataille Premier ME 11111 is a free print and play wargame of Napoleonic warfare. From the introduction:
This document has been provided for the use of all players who strive to enjoy the multiplayer effort of participating in the Age of Napoleon. Yet the rules are flexible enough to facilitate one-on–one play for smaller scenarios and battles—especially corps versus corps engagements.
The authors of this script believe this drama can best be played in the recreation of larger battles, like Austerlitz and Eylau, in which there are a number of commanders for each side. If you are playing with just one other player; or just trying to familiarize yourself with the system; or even playing solitaire, then try your hand with one of the smaller engagements like Auerstadt or Halle. As you gain more confidence with the system, then you may want to escalate to the larger multi-player games where you will be able to experience the intrigue and symphonic dynamics inherent to La Bataille.
This is your script to become a character in a play and the theater is a battlefield in Europe during the early 19th Century. The emotions of tragedy and comedy; glory and humiliation; envy and self-sacrifice; and jealousy and compassion; are an important part of the politics and wars of the period. The authors passionately believe the interaction of human players is the only way to create this drama.