I have worked with many open and proprietary CI tools, and find GoCD to be the best in this space right now. It supports both Continuous Integration and Continuous Delivery. They also made it open source last year:
Well done I guess :) I worked briefly at ThoughtWorks, but definitely don't have any vested interests. ThoughtWorks produces not-so-great products too (like Mingle), but Go CI is definitely a great piece of software. And, I say that as someone who also has used Jenkins a lot.
Also, it's now completely open source. I'm not even trying to advocate an enterprise product.
CI is about the automation of testing code changes before they are merged into the main branch of development. CD is about deploying changes automatically in a live environment.
https://www.go.cd/