To me, Redux is more an architectural pattern than a library. It simplifies (and limits) Flux architecture to single Store per application.
- Extensibility (middleware API),
- Functional programming (state/logic separation, function composition).
- What the Flux?! Let’s Redux by Henrik Joreteg (&Yet),
- The Evolution of Flux Frameworks by Dan Abramov (Author of Redux),
- Dan Abramov's answer to 'Why use redux over flux?' on Stack Overflow.