OCaml

Elixir

elixir-lang/elixir

Dynamic functional language on the Erlang VM for fault-tolerant systems, now adding gradual set-theoretic types.

Scala

scala/scala3

Fusion of OO and functional programming on the JVM, behind Spark and Akka/Pekko; Scala 3 is current.

Erlang

erlang/otp

Concurrent, fault-tolerant language and OTP platform behind telecoms, WhatsApp and RabbitMQ.

F#

dotnet/fsharp

Succinct, functional-first .NET language with strong type inference.

Haskell

ghc/ghc

Purely functional, lazily evaluated language with an advanced type system; GHC is the main compiler.

Clojure

clojure/clojure

Dynamic Lisp for the JVM with immutable data structures and a REPL-driven workflow.