Each user gets a different UID space so every (user × app signature) gets a different UID. I'm not sure what you mean by "fun", this part seems pretty straightforward.
Having mostly-separate data and settings (with a few globals shared between users) is the interesting part, but that's probably equal amounts of fun with either 2 or M+N UIDs.
Copyright © 2017, Eklektix, Inc.
Comments and public postings are copyrighted by their creators.
Linux is a registered trademark of Linus Torvalds