The hms_sys projects will use RabbitMQ as its message-queue provider. RabbitMQ is actively maintained, and is a zero-cost solution, with paid support and consultation options, making it a good low-budget choice. Additionally, there is a ready-to-roll Python library, pika (installed with pip install pika) that provides all the critical functionality needed to send and receive messages from a RabbitMQ server, without having to get too far into the weeds implementing a solution from scratch. The makers of RabbitMQ, Pivotal Software, also offer a commercial version that includes additional management features along with support agreements.
There are other options available for message-queue implementations, ...
