Grand Unifying Guesses/Cyberspace

The creation of ENIAC caused the creation of many worlds including:
ENIAC's younger sibling, UNIVAC, is insanely jealous that it didn't get to create any worlds, and is currently plotting a terrible vengeance. PC and Mac spend nearly every offscreen moment trying to keep the crazy old man in check.
 * The various Digital Worlds
 * Virtual Reality
 * Lyoko (prototyped as Xanadu) and its Replikas
 * The World
 * Sword Art Online and Accel World.
 * Video Land

The following universes are related by having alternate versions of each other's Cyberspace.

 * Tron
 * Re Boot
 * The Digimon multiverse
 * Megaman Battle Network and Star Force
 * Shadowrun (prior to 2064, anyway)

All digital worlds coexist, but use incompatible operating systems.

 * Tron uses Macintosh.
 * Re Boot uses Windows.
 * Megaman Battle Network uses Unix.
 * All the Digimon universes use the ENIAC's operating system, being directly spawned from it.

They all exist simultaniously but never interact with oneanother because they are incombatible with each other. A character from Tron can't travel to a Digimon world because the Digimon operating system can't run the Tron character's program. Attempting to join the digital worlds via the internet creates The Web, as seen in Re Boot, which breaks down the programs of every digital character not native to The Web, preventing the digital worlds from interacting online.

Most Planet Eris and furry webcomics which do not have space travel in them are set in a far-future revision of Second Life
Jossed in the case of DMFA, as that is set in Furcadia...