According to me Facebook is the one of the social media site which will be remain forever networking site. Actually Facebook is the social network where index of life like birth and death can be maintained and it get simplified when feature called timeline get added to it. Am not saying this happens first time in the internet history. Many comes like My space, Friendster and AltaVista but they cant collect the audience like facebook. May be fb will remain long for ever, 901 million users later,its truly something different. May be in future something will come but according to me it cant overtake FB.
I have this 9 apps list which could challenge FB.
Highlight - number of users unpublished)
Path - 3 million users Founded by ex-Facebooker Dave Morin
Pinterest - 11.5 million monthly active users connected through Facebook, according to AppData
Viddy - 36 million monthly active users connected to Facebook, according to AppData
Tumblr - 56 million blogs
Google+ - 90 million accounts, In terms of format, Google's social network is the closest thing to Facebook. But it's not nearly as successful.
Twitter - 140 million active users
LinkedIn - 161 million accounts
Bonus edition: Airtime 0 users