Multi-widget for displaying category listings for custom post types (custom taxonomies).
I'll save you the hassle of downloading the plugin and digging through its source code. Just use the
wp_list_categories() function in your theme (or plugin) to display custom taxonomies as a list, and use
wp_dropdown_categories for a dropdown (this one does require some supplementary html). This plugin is essentially a widget UI shell for these functions. If you want to use the plugin's code for it, go right ahead, but it really does just widgetize those functions.
There is no (need for a) settings page. Simply go to appearance->widgets and drag the List Custom Taxonomy Widget into your sidebar(s) where you want to list the category/taxonomy.
The widgets API can sometimes get messy when I've added features in an update since you first used the widget. If you're having trouble seeing all of the options, first try clicking "save" on the widget, and if that doesn't work you can refresh individual widgets by removing them and creating a new instance (drag a new list custom taxonomy widget into your sidebar and set up the options from scratch).
If you'd like to do something outside of the configuration options of this plugin, look at the WordPress Codex documentation on the function this plugin implements, wp_list categories. If this function can do it, the plugin can do it with minor edits, just look in list-custom-taxonomy-widget.php in the plugin editor. If it's a more universally helpful feature, let me know and I'll add support in the widget UI.