ErlangErlang is a distributed, fault-tolerant, concurrent functional programming language developed by Ericsson. It is worth noting that Ericsson considered both Lisp and Prolog for a project, and opted to create Erlang themselves instead. For over 10 years it has been used in real-life telecommunication applications, but is now expanding to other areas.
The whole development environment and documentation is now available as open source erlang.org, and with lots of goodies such as distributed databases, multimedia gateways , and the first half of the book.
The Erlang programming paradigm is sometimes marketed as "Concurrency-Oriented Programming", which is essentially equivalent to Actors.