Implementations of Reactive Streams

Akka Streams:
- Part of the Akka framework.
- Provides a high-level, composable API for building reactive streams.
Project Reactor:
- A reactive programming library for building non-blocking applications in Java.
- Provides Mono (1 item) and Flux (multiple items) types.
RxJava:
- Reactive Extensions for Java.
- Inspired by the Observer pattern with rich operators for transforming and combining streams.
Spring WebFlux:
- A reactive web framework built on Project Reactor.
Vert.x:
- Reactive toolkit for building distributed systems.