2collab from Elsevier

"2collab is a social bookmarking site where you can store and organize your favorite internet resources - such as blogs, websites, research articles, and more. Then, in private or public groups you can decide to share your bookmarks with others - stimulating debate and discussion. Members of groups can evaluate these resources (by rating bookmarks, tagging and adding comments), or add their own bookmarks. You can browse public groups and bookmarks, but must register (your name and email address) to access the full functionality – such as creating groups, adding comments, and adding bookmarks." 2collab is a free service from Elsevier, initiated by a collaboration between Scopus and ScienceDirect