A sci-fi theme using OD&D rules - nice! And it's free!
It's a little bit like Traveller, with OD&D rules (in my view, anyway); since it has tech levels, etc, slightly similar to Traveller.
Very well written, with helpful sections: Game Master's Guide, World Generation, Adventure Creation, Alien Creation, Spaceship Design, Hydra Sector.
All in all, very nicely done.
Slight niggles: graphically flat; also, each page heading (World Generation, Xenobestiary, etc) has a large black square with the heading in white writing. That large black heading frame will eat up the ink a bit, considering there are approximately 15 or more headings.
But apart from the slight niggles mentioned above, it's very good, and well recommended.
[5 of 5 Stars!]