Tanzanica is a set of free wargames rules for Darkest Africa adventures by Brett Abbott. The rules actually are a variant of Games Workshop’s Mordheim miniatures rules, which are themselves free at the Games Workshop living rules archive. Mordheim is a neat set of rules for the kind of game where each player controls a small group of characters, with one uber-character and several flunkies.
colonial
Structures For Colonial Gaming
Here’s a set of instructions on how to build a variety of buildings for your colonial wargames.
Two Page Skirmish
There is no shortage of free wargames rules for the Colonial period. A good one is the Two Page Skirmish rules from Steve Winter.
Hordes of the Empire HOTT Variant
Hordes of the Empire is a colonial variant of the Hordes of the Things rules. Hordes uses DBA mechanisms.