The document discusses Akka.NET, an actor model framework for .NET. It introduces the actor model, which originated in 1973 as a mathematical model of concurrent computation. It describes key concepts of the actor model used in Akka.NET including the actor system as the root structure containing collaborating actors, how actors communicate asynchronously through message passing, their lifecycles and fault handling strategies. The document also mentions additional Akka.NET modules for remote deployment, persistence, clustering and streams.