'Scholarly' alternatives to Goodreads As you can read on Wikipedia, 


  Goodreads is an Amazon company and "social cataloging" website founded
  in December 2006 and launched in January 2007 by Otis Chandler, a
  software engineer and entrepreneur, and Elizabeth Chandler. The
  website allows individuals to freely search Goodreads' extensive
  user-populated database of books, annotations, and reviews. Users can
  sign up and register books to generate library catalogs and reading
  lists. [...] On the Goodreads website, users can add books to their
  personal bookshelves, rate and review books, see what their friends
  are reading, participate in discussion boards and groups on a variety
  of topics, and get suggestions for future reading choices based on
  their reviews of previously read books.


My question is: 


  Is there a scholarly alternative to Goodreads, that is, a website
  where you can shelf papers, journal articles, scholarly websites, and
  preprints as well as books?
There indeed is plenty of web sites where you can shelf articles, preprints, etc. (Mendeley, Zotero, CiteULike, and so on; a fairly comprehensive list is available on Wikipedia) but if you also would like to have the possibility of adding reviews like in GoodReads, the things are somewhat different. 

One site that I know of that allows you to do this, in addition to merely bookmarking the items, is ResearchGate with its Open Review feature, but you can only bookmark and review items that already are in their database (you can add the articles that you (co-)authored but I doubt that reviewing them is your intention). Perhaps there are some other sites with a similar functionality: e.g. according to Wikipedia CiteULike has it too; on Mendeley you can share articles' annotations within private groups.

Also, there is a number of sites allowing you to bookmark and review arXiv preprints (e.g. SciRate) but not the other kinds of items like the books.