Heise reports that the major change in version from 1.48 to the newly released version 2.0 of the Calibre e-book management software are not apparent in its interface or feature list. However, on the inside the developers have converted the code to the Qt 5 GUI library and thus eliminated quite a few errors which were due to the Qt 4 library previously used. In particular, errors in text display should therefore be a thing of the past. Nevertheless, Calibre 2.0 no longer supports Windows XP and OS X versions prior to 10.7 (Lion). Anyone using these dated operating systems would be better off sticking with Calibre 1.48.
However, the developers of version 2.0 have still added some new features. The software can now also synchronise e-books under OS X with MTP mobile devices (Android phones and tablets). There is a new Mark Books tool that can be used to mark books temporarily. The mark appears as a little pushpin icon next to the book and all marks are automatically cleared by restarting calibre. A detailed version history can be seen in the changelog.