Welcome back, calibre users. It has been two years since calibre 3.0. This time has been spent mostly in making the calibre Content server ever more capable as well as migrating calibre itself from Qt WebKit to Qt WebEngine, because the former is no longer maintained.
The Content server has gained the ability to Edit metadata, Add/remove books and even Convert books to and from all the formats calibre itself supports. It is now a full fledged interface to your calibre libraries.
The change to use Qt WebEngine has entailed a complete rewrite of various parts of calibre, including the E-book Viewer, PDF Output, Book details etc. Every attempt has been made to preserve features and functionality in a backwards compatible way, see below for a list of some known incompatibilities.
Wow, Calibre 4.0 is comming. I can not image how different it is from 3.x.
I can wait to see it. Now download it 115MB. Install it. Then launch it.