Cfait does tasks, sub-tasks, comments, status (to do, done, canceled, started, paused), dependencies, and you could use tags/sub-tags to assign people.

You would need a CalDAV server which allows sharing “calendars” (I’ve only use Radicale and I do it there with symbolic links).

There is an Android and desktop (Linux, Windows, in theory MacOS) TUI and GUI clients but no iPhone. It uses the CalDAV standard so the data would still be accessible from an iPhone using a different client (but it might look less organized especially if that client doesn’t support all the same features).

Disclaimer: I am the developer :)

codeberg.org/trougnouf/cfait