I have been asked for adding custom fields to category or tags. And MB Term Meta is my answer!
This extension helps you adding custom fields to any taxonomy using the similar syntax of Meta Box. You can set category icon, featured image, color or add any custom data you want.
The plugin uses term meta of WordPress 4.4. Make sure you update your WordPress to the latest version before use.
Autoloader for Meta Box Needs Your Test
There has been a lot of questions about loading Meta Box directly in themes/plugins or custom project. We have been working hard on rewriting the way the plugin loads its core and now the new code is available on Github:
https://github.com/rilwis/meta-box
As this is a big change (it might affect your theme/plugin or project), we need your help to test it. Any feedback and suggestion is welcomed!
How to Migrate Custom Fields Data from ACF to Meta Box Plugin 
Introducing SearchWP - Meta Box Integration 
Introducing MB User Meta Extension