Erlang (/ˈɜːrlæŋ/ ER-lang) is a general-purpose, concurrent, functional programming language. It is also a garbage-collected runtime system. The sequential subset of Erlang supports eager evaluation, single assignment, and dynamic typing. Erlang is known for its designs that are well suited for systems with the following characteristics: * Distributed * Fault-tolerant * Soft real-time, * Highly available, non-stop applications * Hot swapping, where code can be changed without stopping a system.