Friend of a friend (FOAF) is an RDF document vocabulary that allows for description of oneself and relationships. It's a bit like a cross between RSS and a directory (think active directory, edirectory, LDAP).
A superficial look at FOAF reveals some appealing ideas, much like my first superficial look as RSS. In retrospect, my first look at RSS missed all the incredible appeal and power that exploded out of RSS as enough feeds became available for aggregation to make sense.
So now I look at FOAF with that experience and wonder if a similar explosion could someday occur.
Ed Dumbill's Developerworks article is a good intro, with links for further reading at the bottom.
Update: Here's a link to the photo demo, in which you can find a photo of someone, then jump to other photos of the people who are with them in that photo.
http://swordfish.rdfweb.org/discovery/2001/08/codepict/
Dated: 07/11/2002