Wargame App that tranparently displays templates on top of vassal. Free for Windows
When you play vassal modules, this app nicely measures and calculates damage areas, like you would on a proper tabletop. The transparency display can use different shapes, be rotated and resize to suit. Examples of use are games like Carwars, that use a turn key, or Warhammer, to see an area of effect after a cannon shot, but my fav is minatures in Vassal.