Star Frontiers is TSRs early foray into the realm of Science Fiction RPGs. It was a system different than D&D in many important ways - first there was no leveling of characters... you are given a set number of hit (health) points and there was no increase as the adventures progressed. Experience was used to buy skills - a nice simple skill system where each skill you bought/earned could be advanced from level 1 (beginner) to level 6 (expert). As such, you could be a techie - taking Computer Skill (lv 1-6), Technician Skill (lv 1-6), etc. Or you could be doctor - taking Medical (lv 1-6). There were, of course, skills to increase your proficiency with weapons, driving vehicles, etc.
The boxed set had two rule sets - a basic rule set which was, admittedly, fairly simple but enough to get you into the game. The Expanded Rules is where things really pick up. There are four playable races in the game: Dralasite, Humans, Vrusk, and Yazirian - they have come together to form a United Planetary Federation (shades of Star Trek).
The game runs on percentile dice - two d10s are rolled to produce a number between 1 and 100. This is used for almost all checks in the game - including combat. Damage is also done using one or more d10 dice. The box sets came with plastic d10 dice which you filled in with a white crayon (also included).
Star Frontiers saw two major publications of box sets - though they were essentially identical except for the cover artwork. There were a number of high-quality adventure modules as well.