Flow

Flow adds static typing to JavaScript to improve developer productivity and code quality. Initially developed by Facebook.

Alternatives

Typescript
https://www.typescriptlang.org/

Redux

Redux is a handy tool for managing state across an application. Although Redux isn’t strictly a Facebook project, it’s very likely had a lot of Facebook resource put into its development.

Alternatives

MobX
https://mobx.js.org
Beedle
http://beedle.hankchizljaw.io/