A category dropdown that will only allow you to select 1 category for an entry.

Developed by Wouter Vervloet, http://www.baseworks.nl/

Drop the entire lonely_cat folder in the third_party folder:

/system/expressionengine/third_party/lonely_cat/

Just like any other fieldtype except that Lonely Cat doesn't have any settings. It will show the categories that are assigned to that particular channel. Nothing more, nothing less...