Reddit - Reddit gives you the best of the internet in one place. Get a constantly updating feed of breaking news, fun stories, pics, memes, and videos just for you.
Raindrop.io - All your articles, photos, video & content from web & apps in one place.
SaidIt.net - Saidit.net - say your truth.
Tagpacker - A free tool to quickly collect, organize, and share your favorite links.
Tildes - A non-profit community site driven by its users' interests
Diigo - Diigo is a powerful research tool and a knowledge-sharing community