CiteULike

CiteULike was a popular web-based service that allowed researchers to store, organize, and share their academic papers. It was one of the first tools to bring social networking to the world of academic citations. Users could tag papers, join groups, and see what others were reading. Unfortunately, the service was shut down in 2019.

While it was a pioneer in the field, it is now obsolete. Users who relied on it have largely migrated to Zotero or Mendeley, which have since incorporated many of the social features that CiteULike originally championed.