Although Yahoo doesn't seem to be doing very well recently, they've done lots of great engineering. I recently looked through the organization's Github [0] and discovered a few nice packages.
I'd happily pay for a good managed CD build system capable of handling projects / products with multiple dependencies.
Right now I use CircleCI along with a bunch of scripts, and it works, but it's not great. One problem with existing CI tools that I've used is they only handle a single git repo, so extra automation has to be done ad-hoc. It's not terribly difficult, but it's tedious and it doesn't give you any kind of safety guarantees.