2.0.0-RC2
This Release Candidate features a large amount of internal fixes, cleanups and enhancements. Please refer to the closed PRs for its milestone. This includes the bugfix for the Single.subscribeOn failing with Disposable already set! error printed to the console (Issue 4448, Pull 4450).
The library now has a new base reactive type: Maybe which is essentially a Single and Completable combined. You can have exactly 1 onSuccess, 1 onError or 1 onComplete signals with it. Note however that it doesn't have all the operators possible for this type of source but you can convert it back and forth to the other base reactive types (i.e., Flowable, Single, Completable and Observable). Unlike Project Reactor's Mono type, this doesn't implement the Reactive-Streams Publisher (but is designed along the idea) and doesn't have backpressure (as there is no chance of buffer-bloat like with unknown length Flowables and Observables).