This plugin offers a quick way to add/remove from the selected books to a specified "user category" via the context menu. A user category (defined using the tag browser panel on the left of the Calibre display) can contain lists of any combination of authors, tags, series or publishers. They allows you to categorize your collection at a "higher level" than per book which can sometimes be a limitation of tags/custom columns.
For more information, see the Wiki
All kiwidude's calibre plugins are now developed and maintained in GitHub at:
Please see the README.md and CONTRIBUTING.md at the above site for more information.