EMQX may be the best choice for handling massive amounts of connections, cause it has been tested with 100 million connections. This resource will tell you the answer to why EMQX is so scalable.
Learning about the benefits of MQTT and how you can have a high-performing and scalable message-broker-based IoT platform up and running quickly from scratch.
Haskell-style functional programming language running on Erlang VM.
Snabbkaffe is a library that helps testing concurrent and distributed systems. It does so by moving the focus from /states/ to /effects/. Developers find bugs by looking at the logs, Snabbkaffe does the same and automates the process. It has advanced modes of testing: fault and scheduling injection. It aims for efficiency: run test scenario once, verify multiple properties.