That's an excellent question. Does HN count?

It certainly bears mentioning, if you ask me.

I've thought a bit about intentional communities --- communes,
utopian towns, and the like

What makes HN work is two things. One, dang's insanely great moderation work. HN's guidelines are simple, opinionated, and tailored to a specific niche user audience. Dang is an excellent benevolent dictator, enforcing the guidelines with world-class skill and kindness.

Two, there's no direct profit motive with HN. Can't underestimate that. It is optimized for user happiness rather than anything else.

These factors work great for an online community but they don't have easy analogues in the physical realm.

There are a slew of smaller, non-dominant, and often quite
small towns to be found around the world, though the US might
be a good exemplar, whose central focus is often a university or
college

These virtually always contrast sharply with surrounding towns,
even for relatively small schools.

I agree that college/university towns in America are generally pretty nice places. Not utopias but generally cooler than others, as a vast generalization.

I always see them as kind of a... unique byproduct of a flawed system.

The average lifetime earning advantage of a bachelor's degree was about $1 million cumulative USD last I checked. So schools can charge a lot of money, and it is still a good deal, and people will pay that money, and the government subsidizes a lot of this via grants and loans.

So you have a gigantic money faucet pouring money into the town, and a lot of people (students, faculty, and graduates who never move away) who have certain demographic traits: they tend be more intelligent and/or more driven and/or are more educated and/or enjoy more privilege.

And that certainly creates a certain kind of place, although I think the key factors are hard to duplicate elsewhere w.r.t. founding intentional communities.

(Although, maybe that is the ultimate lesson: found your intentional community in the shadow of a giant money faucet and/or a privileged niche community)

Another element of the "small" bit

Yeah. Small is key. I founded a (now defunct) online niche community that had a very committed fanbase. I viewed smallness as our moat, actually. Big players could never be as small as us; could never have the "small town" or "local bar" feel. This is still an extremely viable business plan for a lot of things IMO if you are willing to stay small and target a max of like... several fulltime employees. There is a lot you can do with a business if e.g. $250,000-$500,000 is your target revenue and are content with that rather than trying to conquer the world, but that requires you to bootstrap and avoid investors more or less.

I think Reddit's approach was awesome, actually. A bunch of small, mostly-independent communities (subreddits) under a single roof.

It would work if they could downsize and have a razor focus on the core functionality people actually care about. But no, they have to enrich investors, and pay SV rent and SV salaries, and therefore can't turn a profit even on hundreds of millions of revenue.

I hope a leaner operation takes their approach and runs with it. I have seen a few mentioned in this discussion. And the StackOverflow network has AFAIK managed to prosper with an approach that is somewhat similar if you take a 50,000ft view.