React is on everyone's lips right now. And yet it is not even a real framework, but rather a collection of methods and best practices. The innovation is first and foremost a new way of thinking, that strives for simplicity and comprehensibility: the functional approach for HTML.
Because business logic and display are more and more physically separated as well (server communicates with mobile phone), React is rather appealing for mobile app development due to its simplicity. A framework called ReactNative makes sure that React's methods work seamlessly on both iOS and Android.
React is being developed by Facebook and is available without any licensing constraints as of recently.