This framework is built for use in creating real time data intensive applications, with it following an event driven system that keeps it effective yet light weight enough to be perfect for both web or mobile applications. Node.JS is ridiculously extensible and scalable, with it offering a lot of community plugins and tools (Cordova comes to mind) that extend its functionality with Node also just being built to be able to handle a lot before falling over.
What makes this framework popular is the versatility it offers, with it being able to make both front and back end components of an application, and being a framework that allows both the front and back end of an application to be the same language, framework and codebase makes for far faster development and iteration of a web application.
Created and maintained by the team behind Facebook, React is an incredibly popular framework that is used to build responsive interfaces for web applications. React also separates itself from other interface building JS frameworks by using a uni-directional data flow over standard DOM manipulation, which is a lot faster, easier and scalable.