The Tracey Fragments (2007)

Tracey Berkowitz goes on a journey to find the truth behind her little brother Sonny's disappearance. If you like split screen techniques then you’ll be in heaven. About 99% of the film is presented in split screen; there must be at least four movies worth of movie.
It got a little overpowering after about twenty minutes, but by then the story had become so filled with metaphor, both structurally and visually, that I was in for the duration. It requires you to have picked up on certain things said and unsaid before they are fully revealed, and that reveal doesn't come until well into the running length.

Interestingly, a project called Tracey Re:fragmented made all the footage shot for the film available as a download (under a CC licence) so people could remix and re-edit it to create a new truth.

3 bus rides out of 5