Async / Await asynchronous programming model for Java similar to the functionality available in C# 5. The implementation is based on continuations for Java (see my other projects).
EA Async implements async-await methods in the JVM.
Resources for a conference talk on async tools for Java
ArangoDB Asynchronous Java driver
Asynchronous Http and WebSocket Client library for Java
Java utilities for working with CompletionStages
Awaitility is a small Java DSL for synchronizing asynchronous operations
An asynchronous, persistent, key-value storage system for React Native.
Asynchronous Java made easier