Initially, it was developed by a team of engineers at Facebook to be used internally within Facebook, but then later on as developers at Instagram wanted to use this awesome tool in Instagram too, Facebook decided to decouple React from being its proprietary technology to an open-source library.
React is extremely easy to get started with. It doesn't have a steep learning curve, believe it. People generally regard React to be slightly more complex than Vue.js while much simpler than Angular. Regardless, React is intuitive, has a breathtaking potential, and is extremely performant. The most notable features of React include the virtual DOM, the idea of using components to compose UIs instead of templates (as in other UI frameworks), immutability of data, uni-directional data flow, a system of synthetic events wrapping native DOM events, and much more.
The ecosystem of React is also pretty huge and diverse. Once you learn React, you unlock your way into a whole new world full of libraries and tools made to work alongside React and simplify the development process considerably. Learning React can also land you in developing applications for Android and iOS, thanks to React Native.
Today, there is an immense scope of React in the job market out there. Almost every other job lists React as a prerequisite (because it is awesome!). Likewise, investing your time in learning this astoundingly remarkable tool would definitely be a smart choice.
serve from npm, and a couple other related tools.