"Anomalous Variations In Reality"

Many works perhaps tell us of variations in reality. Here we consult just four authoritative texts:

the Time Patrol series by Poul Anderson;
the Old Phoenix sequence by Poul Anderson;
the Nantucket Trilogy by SM Stirling;
The Sandman: Worlds' End graphic novel by Neil Gaiman.

Founders, If Any
The post-human Danellians will found the Time Patrol.
Some power unknown granted the Taverners their charter for the Old Phoenix.
I still do not know whether a higher intelligence or technology moved Nantucket through time.
The Inn of the Worlds' End (see image) is continually being created because worlds are ending all the time.

Since the Old Phoenix and the Worlds' End have much in common, it might be instructive to summarize what we are told about the latter. It is:

the inn at the end of the worlds;
its own place;
what's left when the real worlds end;
not part of the realms of Dream or Death;
a Free House;
no part of any kingdom or empire;
a story, vision or hope;
a refuge after the lights go out, for a while;
a place where dead people sometimes go but do not stay.

There is more.