[Andrew]

Primer (2004). I'd never heard of it until this xkcd comic, did a little reading and decided I wanted to see it. In brief, it's a super-low budget hard science fiction story about a very limited form of time travel.

It takes a lot of attention, and there's a fair amount of Howard Hawks-style fast-talking and talking over each other which makes it very difficult for me to follow (but that's why there's a back button).

I recommend it, especially to engineers, programmers and other geeky types (like me) or anyone with an interest in hard science fiction. If you liked Pi (1998) you will like Primer. When you're done, the Wikipedia page will help make sense of what you just saw, as will this scholarly deconstruction.