I have seen at least two manga where there are multiple series told from the points of view of different characters, but all set in the same world and at or around the same time.
First is chrome-shelled-regios, which includes:
- Chrome Shelled Regios
- Chrome Shelled Regios: Missing Mail
- a couple of others
The other is code-geass which includes:
- Code Geass: Lelouch of the Rebellion
- Code Geass: Suzaku of the Counterattack
- Code Geass: Nightmare of Nunnally
- a couple of others
Where did this originate and what was the first manga/set of manga to showcase this?