The goal is actually that I’m able to hook my ticket tracking system (I’m using Zammad) to various ToDo lists I can expose to other people. I’m happy to write middleware to make that work, but I don’t want to write a whole ToDo app.
Needs to be able to track multiple lists that can be shared in a granular way (I want to share some lists with some people and other lists with other people).
https://tasks.org/ does it with CalDAV, and you can share different CalDAV calendars with different people, fo example in Next cloud fairly easily, but also with Radicals, a bit more manual.