Drone is a self-hosted alternative, although you still have to do some configuration:

https://github.com/drone/drone

We went from Drone -> CircleCI -> Jenkins in the last two years. Jenkins feel opaque and hard to reason about, periodically dies for no _good_ reason and the UI is atrocious.

Drone itself was fine, as a minimal feature set. I think the docs are offline now, but it's fairly straightforward.