QDB is open source message broker software (i.e., message-oriented middleware) that provides a HTTPREST API to persistent message queues. Unlike most message brokers, QDB allows messages to be replayed efficiently by timestamp or id. QDB queues have a configurable maximum size and the oldest messages are deleted when the queue is full i.e. they function as ring buffers. The source code is released under the Apache License 2.0.
QDB can consume messages from and publish messages to other message queueing software and comes with RabbitMQ integration built in. Thus it can be used to backup RabbitMQ queues and replay messages for testing or recovery or push messages to a remote RabbitMQ server (a lighter weight and more flexible solution than using a RabbitMQ shovel).