That's a small example, limited to very small geography, and is really an example of power struggle than of different groups autonomously governing themselves.

Closer to the mark examples are all over the place with different levels of success. The most prominent are the governance structures of multiculutral and multi religious states of south and southeast Asia, Singapore is a prominent oneone, but India and Bangladesh have also adopted similar models to differing degrees. Basically, where multiple ethicities or religions coexist together, their civil and sometimes even criminal law are the laws of their religions or ethnicities, and only when a dispute is between people of disparate groups does some supreme, secular society wide set of laws apply. There are also examples of this throughout Africa, and truly, this is the way most of the world operated for thousands of years before states had defined borders.

Of course, these aren't truly what we are talking about, they're close, but in my examples there is still an overarching state that is arbiter of last resort, and there is nothing voluntary about the associations, they're usually hereditary and imposed by the state with at most an opt out of tribal/religious law. The concept as noted in the diamond age differs in that associations are voluntary (both on the part of the individual as well as the organization) and prominently, you're subject to the law of those you violate, or, if two members of two different groups are in dispute, the dispute and a resolution are handled diplomatically.

> That's a small example, limited to very small geography, and is really an example of power struggle than of different groups autonomously governing themselves.

Definitely a small geography, and, yes, a solution to a power struggle. I'll point out that large parts of of Europe had rather substantial wars and massacres as part of that specific power struggle, and also that this definitely is "different groups autonomously governing themselves".Landsgemeinde are generally viewed as a prototypical example of that, and there was no significant power over Glarus at that time (the Swiss confederation of that time was extremely far from anything like a central government).