The Four Eyed Dog is Dead is a set of free wargames rules for games set in the Taiping Rebellion.
For what it’s worth, the Taiping Rebellion is one of the least known — and at the same time, deadliest — conflict in world history. Taking place in China from 1950 to 1864, best estimates say that the Taiping Rebellion resulted in between twenty and forty million dead.
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.
Days of Empire is a set of free wargames rules for games set in the Crimean War.
Maximilian Rules! is a set of free wargames rules set during the ill-fated Maximilian Adventure in Mexico in 1861 – 1867.
Dog Soldiers is a set of free wargames rules from the old Gauntlet for the plains wars.