RxStream
If all you need is just a stream (RxJS Subject). Very lightweight (1.5Kb gzipped) and tree-shaking friendly.
Installation
Using npm:
$ npm i -g npm
$ npm i --save rxstream
Documentation
Example
import { Subject } from 'rxstream';
let stream$ = new Subject();
stream$.subscribe(value => console.log(value));
stream$.next(1); // 1
stream$.next(2); // 2