The last one to the party, Microsoft's So.cl social network is an "experimental research project" that Microsoft tested on research students before quietly opening to all user today. Unlike Facebook and Google+, So.cl is a social network built mainly to push more content through Bing.
Whereas social networks such as Facebook and Google+ exist primarily as places for users to share self-discovered links, GIFs, and LOLCats, So.cl is "an experiment in open search" that wants to help you find cool share-ables through Microsoft's Bing search engine.
PCWorld's brief walkthrough of So.cl illustrates the social network's workings perfectly:
Let's say you wanted to post an article from The New York Times. On any other social network you would just grab the article link, paste it into your post, type up a comment, and you're done. But not on So.cl.
Instead, you past your URL into a pop-up box that appears after you click "Add link" and hit enter. This causes a Bing search based on your link and then you can choose the article you want to share from the Bing-powered results.
The other way of posting is by just searching for something through Bing. Again, everything shared must go through Bing. Don't like Bing? Tough luck, buddy. Just don't use So.cl.
And according to CNET, searches made through So.cl will be "viewable to other So.cl users and to third parties." That means, don't go searching for nude bikini pics of Jessica Paré (Megan Draper on Mad Men) unless you're okay with your friends knowing that kind of stuff.
Ironically, you actually use your Facebook or Windows Live (soon to be dead) to log-in to So.cl.
Despite it going "live" for all users, So.cl seems to require an invitation if you're trying to access it with your Facebook account. A Windows Live email grants you immediate access.
Go ahead and take So.cl for a spin. When you're done, let us know what you think in the comments below. We're willing to bet it's not for most people.