Named after A. K. Erlang, it was developed at Ericsson for use in telecommunication hardware. It was designed to support distributed, fault-tolerant, soft-real-time, non-stop applications. Since its release as open source in 1998, it became used by companies world-wide, including Nortel and T-Mobile.
Code looks like this:
fac(0) -> 1; fac(N) -> N * fac(N-1).
See also: Erlang unit