calibre: The one stop solution for all your e-book needs. Comprehensive e-book software.

Welcome back, calibre users. It has been a year since calibre
4.0. The two headline features are Highlighting support in the calibre
E-book viewer and that calibre has now moved to Python 3.
There has been a lot of work on the calibre E-book viewer. It
now supports Highlighting. The highlights can be colors, underlines,
strikethrough, etc. and have added notes. All highlights can be both stored in
EPUB files for easy sharing and centrally in the calibre library for easy browsing.
Additionally, the E-book viewer now supports both vertical and right-to-left text.
calibre has moved to using Python 3. This is because Python 2
was end-of-lifed this year. This should be completely transparent to calibre users,
the only caveat being that some third party calibre plugins have not yet been ported
to Python 3 and therefore will not work in calibre 5. For status on the various
plugin ports, see here. This effort involved porting half-a-million
lines of Python code and tens-of-thousands of lines of extension code to Python 3. This
would not have been possible without the help of Eli Schwartz and Flaviu Tamas.

• Highlighting in the E-book viewer
• Dark mode support
• Enhanced search in the E-book viewer
  The E-book viewer now supports enhanced searches with whole word, regular expressions, etc.
  Search results are displayed grouped by chapter. There is a button that takes you back
  to where in the book you were after you are done searching.
• Backwards incompatibilitiesThere are a few minor backwards incompatibilities to be aware of in calibre 5
  • Because calibre has now moved to Python 3, some third party plugins
    will no longer work, until they are also ported to Python 3. For
    status on the plugin porting effort, see here.
  • Because of the support for library wide annotations, the
    database format was slightly changed. While calibre 4.23
    is able to open and operate with calibre 5 databases, older
    versions of calibre may have trouble.

This is an appropriate time to throw out a big thank you to the calibre
community who have contributed selflessly of their energy and enthusiasm
without which many of the features above would never have seen the light of
day.
Note that some of these features were actually introduced during the
lifetime of the 4.x series. This document describes new features as compared
to 4.0
See what was new in previous major calibre releases:
4.0,
3.0,
2.0,
1.0,
0.9,
0.8,
0.7.