Crush The Fascist Vipers is a set of free wargames rules for 6mm WWII games.
Police Action is a set of free wargames rules for 6mm Vietnam games.
De Bellis Horribilis is a set of free wargames rules for The Great War based on DBA.
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.
Furious Reason is a set of free wargames rules that combines Fire and Fury with Age of Reason.