For the past two years I have been using RxJS extensively, in Cycle.js and in other contexts. Recently, TylorS and I have decided to build a new reactive streams library comparable to RxJS, called xstream. TL;DR: we needed a reactive stream library tailored for Cycle.js. It needs to be “hot” only, so users don’t need to think about subscription semantics hidden in drivers. It should have only a fe