The list of social apps, networks, sites—social platforms of all sorts—is growing longer by the day, and as usual marketers scramble to keep up. And try to figure out which ones will resonate with their audiences.

AirTract, a social networking startup offering a single platform that aims to connect people who want to learn or, conversely, share their knowledge, has put together a list ofsocial mediain infographic format.

Its timeline infographic highlights nearly 50 social platforms that have left a mark in social media history. Some are no longer with us (RIP), but others are... and they have become part of our daily lives.

Of course, it can't possibly list all social sites—there are simply too many. (For example, check out this partial在维基百科.)

But to get a good idea of how far and how quickly social networks have developed, check out the infographic: