A group of people who engage in some real-world activity, coordinated entirely online, usually through an online social network. Ad-hoc communities have much in common with online collaborative projects.
Community networks may be the most useful example, but most ad-hoc communities have a certain serendipity and silliness.
SF works which describe extrapolated ad-hoc communities include Neal Stephenson's The Diamond Age, in which participants place themselves in mortal peril, relying on the anonymous rescue by other participants, and Bruce Sterling's Distraction, which contains many variants.
- Geocaching is pure information-age community: GPS plus World Wide Web
- Degree Confluence Project aspires to have a photograph taken from every integral latitude-longitude intersection
- Where's George, one of the first ad-hoc communities, tracks bills; has over $115 million in US currency in its database
- Book Crossing encourages people to register, then leave books for others to find, read, and discuss
- PostcardX, where you register to receive postcards from strangers
- Zipcar, a network of cars reservable online by the hour; the company encourages members to meet and get to know each other