Concurrency Oriented Programming.
Think Massively concurrent systems or lots and lots of processes all talking to each other, each doing a specific thing that relies on the others to complete the system.
See Erlang.
Silas - How is threaded Tcl comparable to Erlang in a multiple processors/machines (clustering?) system? Is Tcl with the thread package able to do high concurrent programming?
NEM - Yes, Tcl can compete with Erlang in high concurrency. Indeed, until recently, Erlang used "green" threads only rather than native threads and so didn't take advantage of multiple processors/cores at all (other than by using multiple OS processes). That has changed now, and I understand recent Erlang runtimes can use several native threads (one per processor/core) to schedule the software threads. In Erlang you would use threads for everything, whereas in Tcl you'd typically use a few threads with each making use of an event loop.