"Social Apps" There are really 2 types of "social apps": pure social apps socialized apps core functionality is social core functionality is standalone; the social is an enhancement
Pure Social Apps These apps often don't exist prior to a network, and are often "super" versions of an existing social network function. Orkut examples: chats, pokes, (s)craps
Socialized Apps These apps often exist before being introduced into a social network, and could stand on their own 2 legs if disassociated from the network. Many are mashups. Orkut examples: music search, games, tests, etc.
To socialize an app, you find a way to take advantage of the 3 aspects of social networks (and OpenSocial):
How can I let a person paint a picture of themselves?
What kind of updates are a person's friends interested in?
How can I let a person share or connect with friends?
Bonus: Take advantage of a side effect.
How can I usefully aggregate the collected social data?
Socialized Apps: Flickr Search & Share See this app in action. Core fn: Users browse and search for flickr photos. Friends: Users share photos with friends that have the app. Profiles: Users pick photos to be their profile picture. Activity Streams: None.
Socialized Apps: Neighborhood See this app in action. Core fn: Users mark current location and favorite locations. Friends: Users share locations with friends that have the app. Profiles: Users pick current location to be shown in profile. Activity Streams: Changing image is shown in stream.
Socialized Apps: TypeRacer See this app in action. Core fn: Users play a game where they type as fast as they can. Friends: Users see friends' ranks, and invite them to races. Profiles: Users' current rank and friends' ranks are shown. Activity Streams: None *Global: High scores across all users are shown.