In-memory message queue with an Amazon SQS-compatible interface
ElasticMQ is a lightweight, fully asynchronous, in-memory message queue implementation written in Scala / Akka. It provides a feature-compatible Amazon SQS REST API interface for testing, local development, or embedded usage. It can persist queues or run purely in-memory and also supports Docker deployment and a web UI.
Simple, distributed message queue system (inactive)
...Because it is intended for relatively simple use cases, it does not provide the full feature set of some enterprise messaging systems, but is often sufficient for many asynchronous or buffered workloads. Over time, the project became inactive and is now archived. Its minimalism and ease of integration made it appealing for smaller or more controlled message-queueing needs.