Whilst this plugin works very well and does exactly what it says, the method of requiring registration to an unrelated e-mail newsletter in order to activate is questionable.
Upon installing and activating the plugin, you are asked to sign up to an e-mail newsletter about getting blog views and other similar stuff. Whilst I understand there is benefit in this to a lot of WordPress users, it shouldn't be compulsory and isn't really in the spirit of WordPress.
http://wordpress.org/extend/plugins/category-manage-widget/
It subscribes you to two newsletters, one of which you can unsubscribe from, the other you can't as it deactivates your plugin.
Disappointing.
I wouldn't use a plugin like this but you can add the following to the code (wp-content/plugins/category-manage-widget/category-manage-widget.php) in order to use it without registering:
...
//check if registered or not
$mbp_cmw_activate = get_option('mbp_cmw_activate');
$mbp_cmw_activate = 1; // <-- Add this line
if ($mbp_cmw_activate == '') {
echo "Please register in the admin panel to activate the <code>Category Manage Widget</code> widget";
} else {
...