What makes this one better than the similar services that already exist?
Is it like FriendFeed? What differs?
It automatically gets your friends from the various networks and the replies go back to those networks in the same way twitter clients work - though for multiple networks.
I.e. it's not a social network like FriendFeed is - it's a client.
I've had the idea to do this type of a site for a while, but realized backtype kinda does (did, not sure after their rebrand) this already. How does friend binder differ?
backtype looks like a search engine to me - we are focused on what your friends are doing.