#zuul is a Project Gating System. That’s like a CI or CD system, but the focus is on testing the future state of code repositories.
A gating system doesn’t just test a proposed change; it tests the proposed future state of multiple branches and repositories with any number of in-flight changes and their dependencies. And the same playbooks used to test software can also be used to deploy it.
Zuul itself is a service which listens to events from various code review systems, executes jobs based on those events, and reports the results back to the code review system. The primary interface for Zuul is the code review system (or systems) so that it fits seamlessly into developer workflows, and a web interface is available for inspecting the current status and browsing build results.
https://zuul-ci.org/docs/zuul/latest/about.html