Twitch

Twitch is a social video platform where gamers can broadcast, watch, and talk about video games.

A spin-out of a famously failed startup (Justin.tv), Twitch lets you watch others play games. Back in 2012, the whole idea struck us as ridiculous, and there was no monetization yet, but first-time founder/CEO Emmet Shear impressed David Cowan and Ethan Kurzweil. Just two years later, Amazon bought Twitch for a billion dollars.