wpquestions.com, ID = 3166

function list_events_by_date() {

    // vars
    $r = '';
    $start_date = '';
    $multi_day_events = array();

    // get all events
    $events = get_posts( array(
        'order' => 'ASC',
        'numberposts' => -1,
        // 'post_type' => 'events',
        'meta_key' => 'start date',
        'orderby' => 'meta_value_num'
        )
    );

    // if there are any events
    if ( $events ) {

        // get the start date of the first event
        $start_date = strtotime( get_post_meta( $events[0]->ID, 'start date', true ) );

        // begin building output
        $r .= '<h2>' . strftime( '%B %e, %Y', $start_date ) . '</h2>';
        $r .= '<ul class="events-list">';

        // loop events
        foreach ( $events as $post ) {

            // re-assign start date variable
            $old_start_date = $start_date;

            // get the start and end dates of the current event
            $start_date = get_post_meta( $post->ID, 'start date', true );
            $end_date = get_post_meta( $post->ID, 'end date', true );
            // convert them to timestamps
            $start_date = $start_date != '' ? strtotime( $start_date ) : $start_date;
            $end_date = $end_date != '' ? strtotime( $end_date ) : $start_date;

            /**
             * process current event
             */
            // check wether we're at a new date
            if( $start_date != $old_start_date ) {

                // start a new section for new date
                $r .= '</ul>';
                $r .= '<h2>' . strftime( '%B %e, %Y', $start_date ) . '</h2>';
                $r .= '<ul class="events-list">';

            }

            // HTML for each event
            $event_html = '<li><a href="' . get_permalink( $post->ID ) . '">' . get_the_title( $post->ID ) . '</a></li>';
            $r .= $event_html;

            // compare start and end date of current event (is it a multi-day event?)
            if ( ( $start_date < $end_date ) && ( $end_date != '' ) ) {
                // save event for further looping
                $multi_day_events[] = array (
                    'ID' => $post->ID,
                    'start_date' => $start_date,
                    'end_date' => $end_date,
                    'html' => $event_html,
                );
            }

        }

        $r .= '</ul>';

        // echo/return the result
        echo $r;

    }

}