Module: Extend "Authoring information"-tab and adding new field to it I'm looking for a way to attach a custom field of my module to "Authoring information"-tab.

Thanks for any hint
Use hook_form_alter(), add your form item to $form['author'] fieldset (see node_form() function), add your own submit function to $form['actions']['submit']['#submit'] array (or $form['#submit']) and you're good to go! And always remember, Form API Reference is one of your best friends!