Pros: Built-in reader software is very good and can read most ebook formats. Built-in conversion software (to convert ebooks between different formats) also works very well if you use the default configurations; also has pre-configured settings for best display for various hardware ebook readers. Constantly updated and improved.
Cons: Downside of constant updates and improvements is a lot of instability, errors, bugs, etc. Help files are only available online and although they are clear for the simple, basic functions, they are simply hideous for everything else, especially when it comes to any changes to the default settings - if you want to make changes, you are in for long hours of internet research and frustration - and even then you probably won't be able to get things to work properly.
Some people like the ebook management feature, but I really dislike it and don't use it - partly because I cannot customize the organization and naming of my ebooks even remotely how I want it, partly because I have never been able to get some features to work consistently, or even at all - perhaps the sheer volume of ebooks I have is too much for this program.
For example, I already have all my ebooks named exactly how I want them and although there is a setting to supposedly tell calibre not to change the ebook names when importing into the calibre library, I can almost never get this to work. Still, well worth getting for reader and conversion features.
License: Free Details...