I built a system which would notify VFX artists when their shot would be played during dailies. Prior to that there would be lines of people waiting outside of conference rooms. Afterwards you would show up, get feedback from the supervisor/director for ten minutes and then leave. When you've got a crew of thousands those time savings add up.

Very simple implementation wise: get the media player to push the playlist together with what was being played to a REST API and then have a webapp poll it (websockets weren't standardised at that point).