Marcus Downing

Add the option for a third column on the Edit Post and Edit Page screens. This is useful if you have a lot of boxes on your edit screen, from custom taxonomies and plugins.
Also adds a pair of mini columns underneath the edit boxes, giving you space for more small boxes.

Third Column

Спасибо создателю плагина. В одно нажатие задача решается этим плагином.
Есть минус: в начале кода плагина идут 2 пустых символа, что вызывает ошибки на сайте. Зайдите в код плагина и удалите их.



Делаем 3 колонки в админке при публикации записи

Adds a third column on the Edit Post screen.

pressupinc

davidbhayes

Only One Category makes sure users only select one category for their post by making the selectors radio buttons, which only allow one category to be selected.
Rather than spend all your time maintaining the editorial style of only putting posts into a single category, this plugin is a quick way for you to enforce that standard. It makes it impossible for a person to accidentally break your site’s layout of functionality by putting a post in multiple categories. They just can’t do it, whether by accident or intention.

Only One Category

Works great

Limits a post to a single category by changing the checkboxes into radio buttons. Simple.

Third Column vs Only One Category