Days of Iron is a set of free wargames rules for games set during the Franco Prussian War. The rules are designed for 15mm figures, with no particular basing system, as long as they are all based alike.
Franco Prussian
Franco Prussian War Rules
Natholeon’s Empires offers a set of free wargames rules for the Franco Prussian War.
Fire and Furia Francese
Fire and Fury Francese, from Nick Dorrell, is a variant of my all time favorite wargaming rules set, Fire and Fury. Whereas Fire and Fury is designed for the American Civil War, F&F-F is for playing miniatures games set in the European wars of the mid 19th century, such as the Crimean War and the Franco Prussian