EventBus
The no.1 event library for Android
EventBus is an open-source library for Android and Java that uses the publisher/subscriber pattern for loose coupling, enabling central communication to decoupled classes with just a few lines of code. It simplifies communication between Activities, Threads, Services and other components while also simplifying code, eliminating dependencies, and overall improving app development speed and quality.
EventBus offers several advanced features, such as jump start, delivery threads, subscriber priorities, and many others. It is specifically optimized for high performance and is small at just ~60k jar. It's been proven by numerous apps with more than a billion total installs.