QWhatsThis depends on an user action - it hides after mouse or key press and it is sqare shaped....

Is some way to subclass something ( Qwidget or Qdialog), put some flags to have control on its transparency, paint something with Qpainter or QgraphicsScene to get something like "comics dialog".
I now only how to remove window decoration from Qdialog but I´m not sure is it good direction to play with some setAttribute() flags.