David Friedman (Milton Friedman's son), has written about how saga era Iceland could be considered libertarian.

http://www.daviddfriedman.com/Academic/Iceland/Iceland.html

His piece on the Amish

http://www.daviddfriedman.com/Academic/Course_Pages/Legal_Sy...

Somali Customary Law

http://www.daviddfriedman.com/Academic/Course_Pages/legal_sy...

See also Neutral Moresnet

https://mises.org/library/anarchy-aachen