RQ (Redis Queue) is a simple Python library for queueing jobs and processing them in the background with workers. It is backed by Redis and it is designed to have a low barrier to entry. It can be integrated in your web stack easily.
enmasse - EnMasse configuration and documentation
IMAP based message broker client
NATS is an open source, lightweight, high-performance cloud native infrastructure messaging system. It implements a highly scalable and elegant publish-subscribe (pub/sub) model.