Proton is a library which aims to give you a reliable and flexible solution to cross-server messaging. It uses your choice of Redis or RabbitMQ. Other methods, such as Plugin Messaging, are either difficult and messy to implement or have restrictions such as the inability to send messages to a server with no active players. Proton is different in that it
1. creates a simple system for messaging between servers and
2. is robust and versatile enough to where you can implement any messaging need you require.
Proton is still being actively developed and tested. Your feedback is welcome.