Not sure it counts as a separate OS, but I run DietPi on all of my pi's. It's a super stripped down version of Debian/RPiOS. Everything you need, nothing you don't.
That’s certainly tricky since the Zero’s CPU supports ARMv6 with VFP2 as that likely eliminates Debian based operating systems unless there is a version with packages built for VFP2 instead of VFP3, like Debian has. Doesn’t look like Ubuntu has had a version that supports the Zero W’s CPU since like 12.04 which is going to be incredibly out of date and unsupported even if it does work.