I don't think there is an obvious one that stands out. Feels like a couple years before one really emerges. Lots of really early stuff in the hype cycle with blockchain, autonomous vehicles, VR, etc. There are also professional messaging platforms (Slack and its competitors) but they don't seem to have the reach yet to enable a huge company on the back of it. Then it seems that most of these are taking a more closed approach to monetize vs the early platforms.