The Portable Wargame project has a set of Colonial Rules. These rules are designed to be played on a square, checkerboard like grid.
Bill Molyneaux offers a set of free wargames rules for fighting the Zulu war.
Sand Pebbles Boxer Rebellion Edition is a set of free wargames rules from Bill Molyneaux.
Richard Bradley offers a set of Colonial Skirmish Rules.
De Bellis Indica is a DBA variant for warfare in India in the 18th and 19th Centuries.