Protocols

• ocaml-zmq – ZeroMQ bindings for OCaml.
• async-zmq – Async wrapper around ocaml-zmq.
• lwt-zmq – Lwt-friendly interface to ZeroMQ for OCaml.
• onanomsg – nanomsg bindings for OCaml.
• Kafka – OCaml bindings for Apache Kafka.
• AMQP – AMQP client library for Async and Lwt.
• MPI – Message Passing Interface bindings for OCaml.
• MQTT – OCaml implementation of the MQTT pubsub protocol.

Security and Cryptography

• ocaml-tls – TLS in pure OCaml.
• Digestif - Hash algorithms (like SHA* or BLAKE2*) in OCaml and C.
• cryptokit – The Cryptokit library for OCaml provides a variety of cryptographic primitives that can be used to implement cryptographic protocols in security-sensitive applications.
• nocrypto – A small cryptographic library behind the ocaml-tls project. It is built to be straightforward to use, adhere to functional programming principles and able to run in a Xen-based unikernel.

Note: The differences between `nocrypto` and `cryptokit` cryptographic libraries are described in the following blog post: OCaml-TLS: building the nocrypto library core.