Erlang
Software / App
Language designed for telecom systems and high concurrency.
Mentioned in 3 videos
Videos Mentioning Erlang

A brief history of programming...
Fireship
Language designed for telecom systems and high concurrency.

Jim Goetz and Jan Koum at Startup School SV 2014
Y Combinator
A functional programming language and runtime environment chosen for WhatsApp's backend due to its scalability and message-passing capabilities.

MIT AGI: Cognitive Architecture (Nate Derbinsky)
Lex Fridman
A programming language used by the Air Force Research Lab to implement ACT-R for parallel processing.