I learned of a college rule today that I had no idea existed and that I'm pretty sure does not exist in the NFL.
If something happens that is not reviewable, but the call was so blatantly missed that replay would easily prove it and it played a material role in the outcome of the game, the refs can at their discretion use replay to overturn it.
The example was in the OU-OSU game today targeting was called on a late interception, and the ruling on the field was that it happened after the pick, which would keep the ball with the defense, ending the game.
Replay CLEARLY showed that the targeting happened well before the pick, and even though it's not reviewable if a flag happened before or after a turnover, they were able to use that rule to overturn it anyway. I thought that was pretty cool, and would be a neat thing for the NFL to implement.