The Category Pie plugin for WordPress adds a pie chart to the administration pages for categories, tags and custom taxonomies. For non-hierarchical taxonomies like post tags the top 10 is displayed.
License
The Category Pie plugin for WordPress is released under GPLv3, you can use it free of charge on your personal or commercial website.
Documentation
Visit the plugin wiki on Github.
Support
Find support at the WordPress support forums.
Contribute
Check out the source code on Github.
Donate
If you enjoy the Category Pie plugin, please consider making a small donation. Thanks!