Kurt Bowker has written a set of free wargames rules set in the Starship Troopers movie universe. I’m not sure where you would get the miniatures to go with these — perhaps Ground Zero Games has something that could be used.
Miniatures Rules
HALO Combat Miniatures Evolved
HALO Combat Miniatures Evolved is a set of free wargames rules based on the HALO science fiction franchise.
Three Musketeers Legends of the Old West Variant
Sgt. Perry’s Heroes offers a variant of the Legends of the Old West rules for miniature wargames set in the era of the Three Musketeers.
Paintingshed Napoleonic Rules
Steve Jones offers his Paintingshed Napoleonic Rules. The rules are written for 6mm figures.
Solar Scourge Science Fiction Rules
Solar Scourge is a set of free wargames rules designed for 6mm science fiction miniatures.