With Mindmap diagrams you can remove the box to show pure text (eg "* _item without box"), eg see here.
Unfortunately this works only with the "bullet item" notation, it doesn't work with the "plus-minus" notation (eg "++ _item without box") as you can see here. Could you make the underscore work with the plus-minus notation?
The space comes after the underscore, not before it.
@startmindmap+_ software++_ projects++_ packages++_ versions--_ DOAP--_ SWO--_ ADMS-SW@endmindmap