Edge of Space is a lovely little d6-based sci-fi system that comes with its own basic space marine setting. Choose from one of 6 professions, then roll 4d6 and consult a table of skills for your profession. Rolling multiples of the same skill gives you more points in that skill. Come up with background and "Strings" that connect your PC with other PCs. Each PC has essentially 4 HP. That's your character.
For the core success/failure mechanic, roll 2d6 and add points in a relevant skill, trying to beat a target difficulty number. The system comes with a set of standard difficulties, from easy (4) to epic (14). There's even a simple mechanic for leveling up.
Most weapons deal 1-2 damage, and all have a range (in meters) and number of rounds.
The game also comes with information on the standard setting, which primarily consists of space marines against sentient alien bugs. You also get stats for 4 of these bugs.
Even better, your purchase includes a PocketMod version of the game, which you can print out for easy transportation and reference.
My only problem with the rules lies in the awkward grammar and odd word choices spread throughout the PDF. For example, the big galactic federation is referred to as a "banding of planetary governments," there are a lot of run-on sentences, and most of the setting description is composed of simple statements in a bland passive voice ("The Confederacy is...A senate is formed...Colonists are average citizens...The Space Marine Corps was formed...."). It doesn't communicate the big space action feel I expected in an action SF system like this. Fortunately, I'm sure this will be resolved in future editions, and it doesn't affect gameplay.