Reactive Future
Reactive Future as implemented in ReactiveFuture class
is a reactive adapter for Java's 
CompletableFuture.
It allows reactive computations to create dependencies on state of CompletableFuture without callbacks or synchronous blocking.
It can also do the reverse: create CompletableFuture that completes when reactive computation stops reactively blocking.
ReactiveFuture serves as a bridge between reactive APIs and CompletableFuture-based APIs.
Download
ReactiveFuture is included in core library.
Documentation
See the ReactiveFuture class in javadoc.
Since the javadoc is not complete yet, you might want to take a look at comments and implementation
in ReactiveFuture.java.