Land of the Lead has a set of one-page Napoleonics Rules. They’re designed for play with a “reinforced division” per side. Scroll down to the bottom of the page to find them.
Rules: Napoleonics
The Immortal Memory
The Immortal Memory is a set of rule for refighting Trafalgar.
Le Baton Napoleonic Rules
Le Baton is a set of free wrgames rules for 15mm Napoleonics.
L’Orre Mixte Napoleonic Rules
L’Ordre Mixte is a Napoleonic Supplement to Fire and Fury.
Regiments and Roundshot Napoleonic Miniatures Rules
Regiments and Roundshot is a set of very simple Napoleonics rules. Interestingly, the instructions call for using a white board for terrain.