Erlang is top contender for distributed app today
Joe designed and implemented the first version of Erlang in 1986 and he currently works for Ericsson AB where Erlang is used to build highly-fault tolerant switching systems.
The above link has links to 2 large size pdf extracts from the book. One is http://media.pragprog.com/titles/jaerlang/Concurrent.pdf
The web site on the open source version: http://www.erlang.org/
Here's a 2007.03.03 blog by Tim O'Reilly on Erlang and other concurrency issues.
Tim mentions that some have found Erlang to be too "old".
TODO learn Erlang
Erlang is called "a pure message passing language". Erlang processes do not share memory. It is excellent for distributed apps but can it be considered a standard multithreaded language? I do not yet know if Erlang has threads where memory is shared.
I recommend that we distinguish standard multithreaded languages where threads share memory from those where threads do not share memory.