Here, you will find links to many online chronologies, timelines, and histories (including a few which I myself have had a hand in creating), and in cases where I am familiar with the subject matter, I have added my own commentary beside the link. They are divided into five media categories:
Television (101 timelines)
Movies (33 timelines)
Books ( 100 timelines)
Games (39 timelines)
Comics (92 timelines)
Also see the dictionary of imaginary places (more like a gazeteer). And the Invisible library of imaginary books.
Or as Borges put it:
Two years ago I discovered, in a volume of a certain pirated
encyclopedia, a superficial description of a nonexistent country; now chance
afforded me something more precious and arduous. I held in my hands a vast
methodical fragment of an unknown planet's entire history, with its architecture
and its playing cards, with the dread of its mythologies and the murmur of its
languages, with its emperors and its seas, with its minerals and its birds and
its fish, with its algebra and its fire, with its theological and metaphysical
controversy. And all of it articulated, coherent, with no visible doctrinal
intent or tone of parody.