RealSpamapS
I run Zuul in production with GitHub and AWS, and it's been really useful for us. It scales to the moon, parallelizes everything, and having all job/pipeline configuration in git means you can test things like CI job changes before they're committed.
Cross-repo pre-merge dependency management means I can build whole speculative futures in PR's before it lands and breaks the build.
Funny story, the Zuul build status badge is just a static image, because Zuul does not allow code to merge if it fails tests: https://zuul-ci.org/docs/zuul/user/badges.html
Full disclosure: I worked on a defunct zuul based service for a little while, and still am a core developer with lots of code in Zuul. A few presentations I've given are here:
http://fewbar.com/the-build-is-never-broken/ http://fewbar.com/zuul-ci-crossing-streams/
It was allowed to stay in unstable:
https://packages.debian.org/sid/mysql-server-5.5
However, the maintainers are uninterested in maintaining it there, since the release and security team have overrode them and forcibly removed it from stable.