As an introvert, the last time I want to see someone who I should make social contact with is when I'm about to arrive home in my private place.
In other words, make sure that the gathering space is not obligatory (at least for introverts): this likely means ensuring that the home in question is inhabited by extroverts.
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The failure mode I experienced in collage common areas was closed/unwelcoming groups of people taking over the room. Notably, one common room transitioning nearly overnight to 'the room where everyone rapidly spoke in (foreign) language X' (I don't remember which language offhand).
This can be mitigated through proper rules; it's not as simple as just having the room available.
I think this depends radically on where you live, how obvious the frontdoor's unlocked status is, etc.
A different way this can be handled btw is to install an electronic lock with a combination-code, which you can give to your friends.
I think the presence of many homeless people is an indication of a broken system. In such a case some of the things like 94 Sleeping In Public just don't work the way they do in a livable city/country.
Other patterns from the book related to getting in contact with friends:
Related: A Pattern Language
Epistemic status: Strong Anecdotal
I'm designing co-housing/co-living communities. The greatest benefit of living near your friends is that you can see each other all the time in low-stakes ways.
If you're living in the same house, this is very easy: you just hang out in the common area and say hi to everyone who goes through. If someone has time to chat then it's an easy way to get a little conversation, but it's not awkward if they are too busy.
This default doesn't really work well in a place where people don't live in the same house or share the same common space. I've spent time in communities where very close friends literally lived on the same block, but they didn't see each other more often than once a week or so, and all interactions require advance planning, because nobody is hanging out in a space where their friends cross through.
To avoid this failure mode, take the biggest or most welcoming house and make part of its common space a true community space. Unlock the door or gate, and let everyone nearby know that it's always ok to come hang out in that space, even if nobody is there. Ensure that you regularly pass through that space. Greet everyone who comes to it warmly.
Follow the intimacy gradient pattern: the unlocked space should be the most public area of that house, nearest the entrance. Try not to monopolize the entire common area of that house -- the people who live there need their own, more-private spaces when they aren't feeling as much like socializing.
You don't need to leave the door unlocked all the time. You should probably lock it while people are asleep. But I emphasize that any barrier against people coming over and hanging out whenever they feel like it will tend to make them dramatically less likely to do so -- subtle signals matter a lot here.
If you don't want to unlock it all the time, you can tell the community about the code to get in, or otherwise allow them to unlock the door on their own somehow.
This might take a while to start working. Some things you could try to go quicker: