I self-host Drone CI still. I think Harness is in the slow process of letting it rot (it still gets at least some updates, though), which is kind of a shame, but it still does just fine for my CI needs (solo usage as well).

https://docs.drone.io/server/provider/github/

Very easy to stand up, does just fine. Definitely doesn't have the "library" of prebuilt actions that GHA does, but for the most part... I consider that a plus.

Otherwise it's very similar in concept - define actions in a yaml file, run commands on an image, webhook integration with most repo providers.

I run it on some old hardware locally (k3s cluster on old machines) and it outperforms the 1000 minutes from GHA easily, and costs basically nothing but some maintenance and time.

I've been keeping my eyes open for something new in this space since Harness bought it, though - so if other folks have recommendations I'd be interested in alternatives.