Use radio buttons for any taxonomy
This plugin lets you switch any taxonomy to a radio-button style metabox, so users can only select 1 term at a time.
A plugin options page allows the user can select which taxonomies she'd like to switch to using the custom radio-button style metabox.
Originally based on the the class by Stephen Harris
Support is handled in the WordPress forums. Please note that support is limited and does not cover any custom implementation of the plugin. Before posting a question, read the FAQ and confirm that the problem still exists with a default theme and with all other plugins disabled.
Please report any bugs, errors, warnings, code problems to Github