Sarah Lacy points at the trend of SnapChat, Whisper, Life360, and NextDoor:

How do you succeed against Facebook? The same way that desktop and small business software companies have always managed to succeed against Microsoft: By finding “white space.” In Microsoft’s most powerful days, that was the first question the press or a VC would ask: Does Microsoft compete with you now, and, if not, how do you know they won’t?

When it comes to  building a consumer Web company around human relationships, the smartest entrepreneurs aren’t thinking niche. They are thinking orthogonal. There’s a difference.

Niche means that Facebook could do it, but you think you could do it better. That’s what loses. What seems to win, so far, are the approaches that do what Facebook couldn’t do, by design.

Look at the core things Facebook does well: photos, connecting you with everyone you know, providing a permanent record, and real identity. These are the exact four things that have made Facebook a powerful company with users and advertisers; these are the four things it can’t betray and hope to succeed.

So among the threats to Facebook, you’ve got Snapchat, which is inherently temporary; Whisper, which is inherently anonymous; and Nextdoor or Life360 (the sponsor of this series), where you can only connect with neighbors or family. Nextdoor is particularly extreme, making you verify residence before you can connect to a network. Many of these are inherently non-viral. Nextdoor at one point relied more on stickers – physical, not virtual, stickers that you put up around the neighborhood – for marketing than on spamming address books.

In case these examples seem too unproven for you, consider LinkedIn. Reid Hoffman always believed, stubbornly and at times against conventional wisdom, that a professional social network was fundamentally orthogonal to a truly social network. For a long time, LinkedIn stubbornly refused to allow you to add photos and until recently didn’t let you add people whose email address you didn’t already know. That hampered its growth in an era when Facebook was hockey-sticking. But, Hoffman argued, it made LinkedIn’s social graph distinctive. Take a look at the company’s performance since it opened itself up to the scrutiny of the public market: Hoffman has been proven right.

Now consider Twitter. It had a core feature essential to its central organizing premise that was orthogonal to Facebook: asymmetrical following. The fact that people could follow you but you didn’t have to follow them was crucial in creating a network that was fundamentally different to Facebook’s.

She misses the other side of social occupied by Tumblr, Reddit, Imgur, and BuzzFeed.

is tumblr just twitter with pictures shown (no need to click)????

Yes. Plus no 140 character limit. And old posts don't disappear like old tweets do.

And Tumblr allows animated gifs. Twitter does not.

And Tumblr's namespace is messed up so it's easier to hide.