Zaqar is a multi-tenant cloud messaging and notification service for web and mobile developers. It combines the ideas pioneered by Amazon's SQS product with additional semantics to support event broadcasting.
The service features a fully RESTful API, which developers can use to send messages between various components of their SaaS and mobile applications, by using a variety of communication patterns. Underlying this API is an efficient messaging engine designed with scalability and security in mind.
Other OpenStack components can integrate with Zaqar to surface events to end users and to communicate with guest agents that run in the "over-cloud" layer. Cloud operators can leverage Zaqar to provide equivalents of SQS and SNS to their customers.
from：https://github.com/openstack/zaqar