Ward St was a cluster of houses in a few block radius centered on a block on Ward St, Berkeley.

The Bailey was the initial house (if Katja recalls correctly). One member moved out and founded another house two doors down. The Bailey's landlord had numerous properties nearby, which suggested an opportunity for this. The experiment was at least partly caused by Katja Grace (here) and Scott Alexander (here) blogging about it.

• There were about seven houses at some point.
• There was little inter-house intermingling to Katja's knowledge
• Houses contained fairly different people and vibes, and many people didn't necessarily know people at other houses that well

• Something like this probably benefits a lot from one common area that everyone feels comfortable going to, with other plausible reasons to be there (e.g. coffee, cereal), like a dorm dining hall. Otherwise there is not much impetus to see each other unless people are comfortable enough just appearing in one another's houses, which is a high bar.
• Neighborhoods are trickier than houses because original members have no control over who joins (though also in this case did not try to exercise control)