OTP is a collection of useful middleware, libraries, and tools written in the Erlang programming language.

[2][3] The OTP distribution is supported and maintained by the OTP product unit at Ericsson, who released Erlang/OTP as open-source in the late 1990s, to ensure its independence from a single vendor and to increase awareness of the language.

[5] In the same year, following the collapse of another gigantic C++-based project, Open System was ordered to provide support when it restarted from scratch using Erlang.

[2] The result was the highly successful AXD301 system, a new ATM switch, announced in 1998.

OTP has also become a specific product unit within Ericsson since then, providing management, support and further development.