Games Workshop’s Warhammer miniatures rules have been adapted to a wide variety of other periods. You can get the Warhammer ‘Nam rules by joining the Yahoo Group.
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Gemini Rules For Warhammer 40K
The Gemini rules for Warhammer 40,000 are essentially a set of house rules for Games Workshop’s flagship product.
I think that the author is correct in his premise — that the Rogue Trader rules were perhaps the best.
Death Squads 41st Millennium Rules
Death Squads is a set of rules for small scale skirmish conflicts in the 41st Millennium.