Wikipedia: Erlang programming language

Erlang is a general-purpose Programming language and runtime? system. It is also available as a Open Source implementation. Named for A. K. Erlang, it is used in telecommunication hardware from Ericsson. It is suitable for distributed and soft real-time systems.

Code looks like this:

-module(fact).
-export([fac/1]).

fac(0) -> 1;
fac(N) -> N * fac(N-1).