Ask HN: What's the best FRP library you worked with?

I have been using RxJS for nearly 3 years now and have a definite love/hate relationship towards it. Most of the time it feels like we're using it, because there's really nothing better out there for JavaScript with that level of popularity and maturity. The definite challenges include complexity and testability.

I've been wondering what other people use in different languages and what are the innovations and better ways to apply this programming paradigm.