Another container based option is Screwdriver, which started as a Yahoo in-house solution built on top of Jenkins. But it is now fully open source and no longer makes use of Jenkins in any way:
This looks really good! For a long time Jenkins has seemed like the only option for flexible jobs. Tools like Drone and Travis and the many other that use a "config file" approach just aren't able to scale against your needs. They're fine for a run-of-the-mill build but that generally just isn't enough.
Drone is working on support for Starlark, a python-inspired configuration language used by the Bazel Build system [1]. For complex pipelines, this should be more analogous to Jenkins scripting and may improve scaling Drone for larger projects (time will tell).
http://screwdriver.cd/