The Iron Hand site has a tutorial on building a very nice building-sized laser defense battery for 25mm – 28mm science fiction games, such as Warhammer 40K. These would be great as the focal point of a scenario.
Miniatures Rules
Galactic Heroes Star Wars Rules
Galactic Heroes is a set of rules for playing game set in the Star Wars universe. The author uses those chunky three inch “Star Wars Galactic Heroes” figures, but any would work well. The author writes:
Galactic Heroes is a friendly game for 2-6 players, ages 6 and up. Each turn, players move their action figures around the table, exploring by flipping over Tokens that could be an enemy, a trap, or even something valuable. When a player successfully deals with an encounter, they collect the token. When all the tokens are collected, the game ends and the player with the most tokens wins!
Johnny Tremaine Johnny Reb Variant
Johnny Tremaine is a variant of Johnny Reb, created with the permission of the Civil War game’s author, John Hill.
Axles and Allows Car Combat Game
Axles and Alloys is a set of free wargames rules for futuristic vehicular combat.
Ravaged Worlds Science Fiction Rules
Ravaged Worlds is a set of free wargames rules for all manner of science fiction adventures.