hauxh

This plugin allows you to require a secret key that is passed via the URL: http://example.com/post-title/?key=[string] 
Specify the key in a custom value called “key” with the [string] or use the built in widget.
Stable version of the plugin are pushed to the WordPress repository, 
but the latest version of the plugin can be found at: 
https://bitbucket.org/excion/wpkeyme/
Issues/Bugs: https://bitbucket.org/excion/wpkeyme/issues

WPKeyMe

This plugin allows you to require a secret key that is passed via the URL: http://example.com/post-title/?key=[string]

tonio7788

This Widget Plugin enables a list or dropdown of categories if the url contain a determinate string.
Features:
<ul>
<li>Choose your category</li>
<li>Select which categories to use the widget on.</li>
<li>Entry the url conditional string that determines if or not the menu appears</li>
</ul>
If you like this plugin, remember to vote 🙂
<a href="http://www.pixel-conception.com/menu_url_plugin_wordpress.html" rel="nofollow ugc">plugin home page</a>

Url Conditional Category List Plugin Widget

This Widget Plugin enables a list or dropdown of categories if the url contain a determinate string.

WPKeyMe vs Url Conditional Category List Plugin Widget