This document discusses Akka, an open-source toolkit for building highly concurrent, distributed, and resilient message-driven applications on the JVM. It notes that Akka uses an actor model with no shared data and asynchronous message passing between lightweight threads. The document lists some of Akka's key features like local and remote actors, typed actors, finite-state machines, logging, futures, events, routing, software transactional memory, REST integration, and support for Spring, Apache Camel, and clustering with fault tolerance capabilities.