The classic WRG Infantry Action 1925 – 1975 rules are available free for the downloading. These are the June, 1972 edition of the rules. The link opens a pdf.
modern
Bekaa Blues Modern Micro Armor Rules
Bekaa Blues is a set of free wargames rules for 1/285 micro armor battles set in Lebanon in 1982.
Go! Go! Go! First Person Shooter Miniatures Game
Go! Go! Go! is a set of free wargames rules modeled on the computer game Counter Strike.