QDB
QDB is open source message broker software (i.e., message-oriented middleware) that provides a HTTP REST 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.