Port Nova Media have released a free version of their Strike Legion sci-fi rules.
From their website:
Command a combined arms ground force from any future you wish to imagine! Strike Legion combines simple game mechanics with a unique, integrated electronic warfare system and a respectable amount of unit detail and variation – and all without sacrificing playability.
Strike Legion scales combat at 1 piece = 1 vehicle, infantry team, or gun, with each turn representing about five minutes of real time. While Strike Legion is designed primarily for 1:285/1:300/6mm forces, players can easily use miniatures ranging from 2mm up to 15mm to fight their battles.
The free ‘Plain Brown Wrapper’ version of Strike Legion contains the complete basic rules section from the Strike Legion main rulebook, along with all the other components you need to begin playing futuristic armor vs. armor engagements (except miniatures and table space, of course).