Erlang
Erlang is a general-purpose, concurrent, functional programming language and runtime environment designed for building highly available, fault-tolerant, distributed systems. It was originally developed by Ericsson for telecommunications applications, featuring built-in support for concurrency, distribution, and fault tolerance through lightweight processes and message passing. The language is known for its 'let it crash' philosophy, where processes are isolated and can fail without affecting the overall system.
Developers should learn Erlang when building systems that require high concurrency, low latency, and extreme reliability, such as telecommunications, messaging apps, real-time bidding platforms, and distributed databases. It is particularly valuable for applications where uptime is critical, as its process isolation and supervision trees allow for self-healing systems. Use cases include WhatsApp's backend, RabbitMQ message brokers, and financial trading systems.