Shane Carruth’s no-budget mind-bender Primer falls into a similar category as many titles on this list: critically lauded, with a cult following, but under seen and largely unknown outside of certain small circles. When four engineer friends stumble upon a method of time travel, they, of course, use it for their own gain, opening up a wormhole of ethical issues. The timeline of all of their various jumps to the past, together and in secret, is so intricate and layered that, more than ten years later, it is still the subject of debate and discussion and countless elaborate infographics. Damn near homemade, but with every shot absolutely essential, Primer takes a standard central idea and uses it to lay these characters bare, forcing them through an ever-twisting, ever-changing philosophical and moral maze. I’ve watched it multiple times and I’m still not sure what the hell is going on.