POLAR - A powerful document manager for Mac, Windows, and Linux for managing web content, books, and notes and supports tagging, annotation, highlighting and keeps track of your reading progress.
Goodreads - See what your friends are reading.
Periodical - This application calculates the fertile days according to Knaus-Ogino.
LibraryThing - A home for your books.
Always Reading - Queue up articles and schedule when you want to read them.
BookSloth - Book Sloth lets you add books, post and see reviews as well as interact with other readers.