Reasonable Brom is a variant of Larry Brom’s standard rules for the 19th Century.
Taiping Era is a set of free wargames rules for the Taiping Rebellion and the Opium Wars. The game is designed to be played with 15mm figures on a game area with 6″ square grids.
Corpen 1899 is a set of free wargames rules for 19th Century naval combat. The author writes:
Corpen:1889 is a set of rules for simulating naval battles in the late 19th century. It was inspired by GDW’s excellent Ironclads and Ether Flyers (I&EF) supplement for the Space:1889 role-playing game. It tries to preserve the “flavor” of that era that I&EF conveyed, while at the same time requiring less dice-rolling and record-keeping than I&EF did. It is based upon my earlier Corpen 18 WWII surface naval combat game, with significant alterations which were required to take into account the much different nature of naval combat in the late 19th century.
Cuirassiers 1700-1870 is a set of free wargame rules for 18th and 19th century warfare. It is ideally for 6mm figures.
David Wareham offers a set of free wargames rules for the 19th Century along with army lists. Scale is 1 figure to 30 men.