Thanks. So it sounds like the SF Xtreme is an add-on\extensions of HARP SF and not a complete rule book that stands by itself, correct?
From what I can gather you would pick up both books and then select which technologies\features you wanted to include in your game and ignore the rest. For example, I could select modern weapons (firearms etc.), cybertechology, and modern vehicles (cars etc.) but ignore lasers, spaceships, and psonics (unless I wanted to use this instead of the magic system from HARP).
Are my assumptions correct?
It actually goes a bit further than that. HARP SF divides various types of technologies into 6 stages of development: Unavailable, Prototype, Early, Mature, Advanced and Obsolescent. To at least some extent, you can tweak not only what's available, but its weight, bulk, expense, power needs and performance specs according to where it falls along that development path.
For example you could decide that the hand held combat capable maser is invented
during your campaign. But being still in prototype it's bulky, hideously expensive, temperamental, sucks power like mad and there are only a few (possibly
one) world wide. It likely wouldn't figure directly into game combats, other than as possibly t
he cause of some, as prototypes get stolen for espionage purposes. It could probably be a really nasty item... but only in the hands of the inventor, because it's a kludged together piece of crap
that in all the world only he's competent to run yet.
But on the other hand, 5 years later they might be the equivalent of the old "brick" cell phones, and if you're willing to pay for it you can get one. 20 years after that there's half a dozen for sale in every sporting goods store.