Inferno

React-like API, concepts and component lifecycle events. Switch over easily with inferno-compat.

One of the fastest front-end frameworks for rendering UI in the DOM, making 60 FPS on mobile possible.

Isomorphic rendering on both client and server, along with fast-booting from server-side renders.

Inferno is much smaller in size, ~8kb vs ~30kb gzip.
Inferno is considerably faster than React. This doesn't apply to only benchmarks, but real-world applications that companies have converted to Inferno from React.
Inferno doesn't have a fully synthetic event system like React does, instead opting to only delegate certain events (such as onClick).
Inferno doesn't support React Native. Inferno was only designed for the browser/server with the DOM in mind.
Inferno doesn't support string refs – although this can be enabled using inferno-compat. We don't recommend using them, they are the source of many memory leaks and performance issues in real-world apps.
Inferno provides lifecycle events on stateless components. This is a major win for people who prefer lightweight components rather than ES2015 classes.
Inferno is able to use the React Dev Tools extensions for Chrome/Firefox/etc to provide the same level of debugging experience to users of Inferno via `inferno-devtools`

There is an Inferno Slack group where you can ask questions and find out the latest news about Inferno development. You can join via inferno-slack.herokuapp.com.