The /sites route can return
site state stand for and which values can it have?
The values I found:
This is related to the lifecycle of a Stack Exchange site; most new sites start as private betas, become public betas and eventually graduate to a regular site.
There's also a value
closed_beta, as documented here.
normal: this is the default state. Beta sites end up here after they've graduated, before they get a design but not upon losing the beta label because of their age. Meta Stack Exchange is also considered a normal site, presumably because it's not linked. Examples: Stack Overflow, Mathematics Stack Exchange, Stack Apps, Arduino Stack Exchange, Ask Patents
open_beta: all sites which are in public beta but haven't graudated. Examples: Chess Stack Exchange, Lifehacks Stack Exchange
closed_beta: sites which are in 'private beta' (currently none), and CS50 Stack Exchange which is in public beta but retained its private beta privilege levels
linked_meta: a 'per-site meta', which is linked to a main Stack Exchange site. Examples: Meta Stack Overflow, Mathematics Meta