RabbitMQ is an open source version. Message Queue Architecture was the hottest thing 20-30 years ago in government. That’s what Estonia implemented (still using), but it all got captured by proprietary vendors that made it stinking expensive and restrictive. I am still trying to remember that name of the vendor that captured it all (still trying). Eventually the dotcom craze made it uncool.
Over the longer run, there were open source versions like RabbitMQ - successful- but now I see NWC blowing the doors wide open on the architecture.