The problem of all the social networks thingamagigs that have arised lately is the lack of expresiveness. You can invite friends
, you are asked whether this person is a friend
or not, you are shown your list of friends
. But there are many kind of friends. You have the friend you would share a couple of beers with. The one you would invite over for dinner. Or for a sleepover. There's also a whole class of friends-you-could-interchange-bodily-fluids with; depending on the time, amount, and commitment, this could become a class of its own.
And relations are not limited to frienships. There are enemies. Imagine having a place where you can list all your enemies, and, with a single click, breath fire on them. Or send also a message to all the enemies of your enemies, who, by definition, are your friends. Or check their likes and dislikes, and make them automatically your diskiles and likes. Know their whereabouts, and avoid them purposefully.
This would be definitely the internet killer app: foester
Remember you heard it here first.