For Genesis child themes that output HTML5 only.

This plugin adds an entry field just below the title field on all post,
page and custom post type edit screens. It allows you to specify a
subtitle for the content and then outputs the result in an H2 tag just
under the entry-title where you’d expect to find it.

This plugin is for use with Genesis HTML5 child themes only because it
uses the hook, genesis_entry_header to position the output after the
title but before the post-info.