Erlang is a programming language originally developed at the Ericsson Computer Science Laboratory. OTP (Open Telecom Platform) is a collection of middleware and libraries in Erlang. Erlang/OTP has been battle tested in a number of Ericsson products for building robust fault-tolerant distributed applications, for example AXD301 (ATM switch). Main developer and maintainer is the Erlang/OTP unit at Ericsson.
Since OTP 18.0, Erlang/OTP is released under Apache License 2.0. The older releases were released under Erlang Public License (EPL), a derivative work of the Mozilla Public License (MPL).