Welcome back, calibre users. It has been almost three years since calibre 2.0. In that time lots has happened. The biggest new feature, which was in development for almost that entire period, is a completely re-written calibre Content server.
The Content server allows you to wirelessly browse your calibre books on any modern phone/tablet and even read the books right in your phone browser. The books are stored in off-line storage on the phone so you do not have to keep calibre running or have an always on internet connection to read the books.