Each tribe have an implicit leader that bears no title yet influences all decisions just by regular social interractions.
Tribes communicate, negociate even, through the implicit leaders even if not directly.
Some kind of overuling bdfl also oversees all tribes, like a king, in case of conflict or emergency. Often the CEO.
It's not "flat org", it's just good ol' human society.
Rules are less clear, social skills are more required and if you get there in the early days you get a big advantages over the newcomers.
But if you get a nice tribe, things rock.