Full Thrust: Project Continuum is a SciFi Strategy Wargame. Not really my cup of tea, but I'm sure there are plenty who feel otherwise. A quick search says that Full Thrust is available for free, and I don't know how this version fits into the series, but the title page states they have proper permissions from the Copyright holders. It appears that this flavor is combination of two earlier rulesets with a generous helping of house rules.
Cool thing is, if you like what you see here, you can go straight to Ground Zero Games and pick up the earlier rulesets for free. GZG is the place you'll want to pick up *official* starship models. I'm guessing that's where they make their money, so that's a big part of why these rules are free.