The Infinite
“The Infinite” was a “bridge between realities”, with an endless starry night sky and a simple, even, black floor.
It had a connection to Jenny Everywhere's shifting powers; one way for her to shift was to pass through the Infinite, which she would always find filled with a crowd of her other selves. Most were only passing through, but some resided there permanently, performing “various tasks”. (COMIC: The Jenny Everywhere Chronicles) Jenny could also mentally tap into the Infinite to view potential events, without physically going there. (COMIC: Governing Council)
Only Jenny Everywhere could travel to the Infinite; it was normally impossible for other shifters to enter it. However, while desperately looking for Jenny after she disappeared from all of reality without explanation, Jenny Anywhere and Hakhe combined their skill at modulating shifting with Laura Drake's bond with Jenny and Jenny Somewhere's genetic kinship with Jenny, and managed to force a shift into the Infinite. Michael Wherever and the Illumination also managed to fly the Wilson into the Infinite by “connect[ing him]self, a cache of Jenny’s genetic makeup, and a ludicrous amount of power to the ship’s computers”. (PROSE: The Disappearance of Jenny Everywhere)
It is also seen in passing in COMIC: Rail Shift.
Behind the scenes
As he noted in a convention panel, Benj Christensen did not initially mean for the Infinite to be an open-source concept. However, he was surprised but happy to see other people start to use it, seemingly under the assumption that it was part of the Jenny Everywhere “package”, and eventually released it into the public domain to join Jenny herself.