AMMDI is an open-notebook hypertext writing experiment, authored by Mike Travers aka mtraven. It's a work in progress and some parts are more polished than others. Comments welcome! More.
This trope is having a moment – the 2022 file Everything Everywhere All at Once is a fucking brilliant use of it, His Dark Materials was based around it, there's a marvel movie, and a zillion other uses (see The Multiverse - TV Tropes)
Trilogy of fantasy novels by Philip Pullman. I'm a big fan.
It must be said that the theology framework is a bit iffy: The Devil’s Party | Alan Jacobs | First Things. It sounds great -- "The Republic of Heaven". But as Jacobs points out, the whole plot is pointed towards a confrontation with the forces of God and the republican rebels, on a scale equal to Satan's rebellion. This doesn't really come off, God is weak and his forces are cartoon villains, the actual meaning of a rebellion against god gets lost in a sort of simpleminded village atheism.