The main difference between a thread and an Erlang actor is that with threads you have to manage resource sharing with locks and with actors you don't share resources. Instead you pass the needed data to each actor through messages. The end result is that it's way easier to manage concurrency through actors rather than threads. It also buys you more features; imagine being able to access all of the actors of a cluster of machines or determining what to do when an actor fails (eg restart it or fail all other actors under the same actor supervisor). I feel that the closest thing to the actor model in the thread world is probably Java's Executor (minus the cool features)

You can do actor model concurrency on Java (and Scala) with the Akka framework (http://http://akka.io). It's a pretty mature one as well. I've been using it for a while now.