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Erlang/OTP

A functional language built for concurrent, fault-tolerant systems.

Erlang was developed at Ericsson in the 1980s for telephone switches that needed nine-nines reliability — at most 31.5 milliseconds of downtime per year. The language and its OTP (Open Telecom Platform) framework are designed around lightweight processes that crash and restart cleanly, message passing as the only inter-process communication primitive, and hot code loading so software can be upgraded without taking the system offline.

Joe Armstrong, Robert Virding, and Mike Williams created Erlang between 1986 and 1991. Ericsson released it as open source in 1998. The BEAM VM is the runtime that Erlang and the more recent Elixir share; both languages compile to BEAM bytecode and can call each other's libraries seamlessly.

Erlang underpins large messaging systems including WhatsApp (famously running fewer than 50 servers for hundreds of millions of users in the early years), RabbitMQ, ejabberd, CouchDB, and Discord's voice infrastructure. The language is small but distinctively shaped — pattern matching, immutable data, and the actor model all feel different from mainstream languages.

Debian/Ubuntu: sudo apt install erlang
Fedora/RHEL:   sudo dnf install erlang
Arch:          sudo pacman -S erlang
macOS:         brew install erlang