Autodesk is the workd leader of 2D and 3D design software. Their most popular programs are AutoCAD, Revit, Inventor and 3DS Max.
Many people are unaware that Autodesk has created the "Autodesk Exchange Store" which provides free and paid add-ons (apps).
So before you program your own tool or hire a programmer to create an add-on/plug-in goto: http://apps.exchange.autodesk.com/.
