Hierarchical Select

In this example, the dropbox is enabled, and nothing else, because nothing else makes sense for this special implementation. The Flat List implementation allows you to pass in an array of options, like with a normal select, and get Hierarchical Select's superior user interface for selecting multiple items.
Show config

Array
(
    [module] => hs_flatlist
    [params] => Array
        (
            [options] => Array
                (
                    [0] => the thing that makes hierarchies fun
                    [1] => an awesome widget
                    [2] => a valuable addition to Drupal
                    [3] => a timesaver
                    [4] => a solution to my scalability frustrations
                    [5] => a small revolution on its own
                )

        )

    [save_lineage] => 0
    [enforce_deepest] => 0
    [entity_count] => 0
    [require_entity] => 0
    [level_labels] => Array
        (
            [status] => 0
        )

    [dropbox] => Array
        (
            [status] => 1
            [limit] => 0
        )

    [editability] => Array
        (
            [status] => 0
        )

    [resizable] => 1
    [render_flat_select] => 0
)