[mkl]

I would like to recommend Timecode (2000) [1]. The screen is divided into four quarters, each containing a single 93 minute take, all shot simultaneously. A camera will follow one person into a room and follow another one out, or you end up with multiple cameras showing different angles of the same events, or four completely unrelated events. Careful audio mixing and timing guides your attention.

[1] https://en.wikipedia.org/wiki/Timecode_(2000_film)

[cbm-vic-20]

I saw this one in a theater when it came out. The audio effects were really good. IIRC many scenes were on an open set, in the streets of LA, so the actors and cinematographers had to deal with that in real time.