@akarnokd I didn't know about Reactor Core until you mentioned it. But even after reading, I can't quite get what it is trying to do. Is it just trying to be really fast and lightweight? It looks pretty similar to RxJava2.
The deal is this, RxJava 2 couldn't go beyond Java 6 due to Android and Pivotal/Spring needed something leveraging Java 8. After some R&D and collaboration with the Pivotal guys on an experimental precursor to both, I did most RxJava 2 and contributed a lot of Reactor. They later moved on with additional features such as context.