Erlang

Erlang is a general-purpose, concurrent, functional programming language and runtime environment designed for building scalable, fault-tolerant systems. It runs on the BEAM virtual machine and compiles to bytecode that can be executed on multiple platforms.

A core strength of Erlang is its lightweight processes and asynchronous message passing. The runtime provides a highly concurrent execution model in which thousands or millions of processes can run simultaneously, communicating solely through messages. This design supports distributed computation across multiple nodes, with built-in facilities for fault isolation and recovery.

The language emphasizes functional programming with immutable data, pattern matching, and higher-order functions. Code is organized into modules, and functions are exported for use by other modules. Erlang also supports hot code swapping, allowing changes to be made to a system without stopping it, which is valuable for high-availability applications.

Open Telecom Platform (OTP) is a companion set of libraries and design principles that extend Erlang for building robust systems. OTP includes abstractions such as GenServer, GenEvent, and GenFSM, as well as supervision trees and application lifecycle management. These components facilitate fault tolerance, process supervision, and structured application architecture.

History and usage: Erlang was developed at Ericsson in the 1980s by researchers including Joe Armstrong, Robert Virding, and Mike Williams to address reliability needs in telecommunications. It became open source in the late 1990s. The language and its OTP framework have been used in telecoms, messaging, and real-time systems, with notable deployments in chat servers and large-scale messaging platforms such as WhatsApp.