3:16 Carnage Amongst the Stars
This was one of the first indie games I bought, read, and learned all by myself. I attribute this to my love of the Starship Troopers film.
Though a bit of a one-trick pony, this game shines either as a fun one-shot, or a surprisingly provoking campaign. The simplistic mechanics revolve around rolling to see not if you kill poor hapless aliens, but how many.
The setting is briefly laid out (you kill aliens for the glory of Terra, a home to which you can never return), but there's a serious disconnect between the setting and the system. In other words, killing aliens is fun and all, but applying themes and story and consequences is purely in the hands of the GM and players. If you're looking for a system to support and drive a good story, look elsewhere.
That being said, I wrote up some campaign notes for the only two sessions I ended up running. Download below.