What’s the website equivalent of a street cafe?

From Christopher Alexander’s A Pattern Language: Towns, Buildings, Construction, a book on architecture published in 1977…

The street cafe provides a unique setting, special to cities: a place where people can sit lazily, legitimately, be on view, and watch the world go by. Therefore: encourage local cafes to spring up in each neighborhood. Make them intimate places, with several rooms, open to a busy path, where people can sit with coffee or a drink and watch the world go by. Build the front of the cafe so that a set of tables stretch out of the cafe, right into the street. The most humane cities are always full of street cafes.

The more thought I give the above quote, the more I’m intrigued by it. As I think about my favorite locales in my favorite cities - Boston, Montreal, Narragansett - they all share one thing in common: lots of places where strangers can congregate and intermingle.

In Boston and Montreal, it’s shops and cafes. In Narragansett, it’s beaches and family-owned restaurants and bars.

I wonder, what’s the website equivalent of a street cafe?

I don’t mean at the internet-level, where the answer is almost certainly Twitter, but at the individual website level. How do you encourage people to hang out and interact?

Notes & Further Reading

1. This post was inspired by Design Patterns: When Breaking the Rules is Ok: http://uxdesign.smashingmagazine.com/2012/06/06/design-patterns-when-breaking-rules-ok/
2. Christopher Alexander's A Pattern Language: http://en.wikipedia.org/wiki/A_Pattern_Language