Erlang

Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability. Some of its uses are in telecom, banking, e-commerce, computer telephony and instant messaging. Erlang's runtime system has built-in support for concurrency, distribution and fault tolerance.
Site: https://www.erlang.org/

Books

Added Stuff Goes Bad: Erlang in Anger

This book intends to be a little guide about how to be the Erlang medic in a time of war. It is first and foremost a collection of tips and tricks to help understand where failures come from, and a dictionary of different code snippets and practices that helped developers debug production systems that were built in Erlang.

 Free book

Added Learn You Some Erlang for Great Good!

Erlang is the language of choice for programmers who want to write robust, concurrent applications, but its strange syntax and functional design can intimidate the uninitiated. Luckily, there’s a new weapon in the battle against Erlang-phobia: Learn You Some Erlang for Great Good!

 Free book