Comment by Natsu

This kind of thing made me imagine the creation of "digital towns" the other day.

Imagine an online community where you can only join on the recommendation of two other members, who you must have actually met in person, to participate. Meanwhile, you leave at least some of the activity publicly available to the general public so that interested parties can meet up IRL and join.

This could probably be implemented easily on top of existing online platforms like Discord, Reddit, etc. since it's really just a community building rule, not a community itself.