OK, it isn't that secret but Autodesk Design
Review is free and can be used for more than "Review". Here's a couple of real world scenarios;
- Can we fit "X" in there? Say you want try options for a tenancy. Could start up CAD or just use the Area tool in ADR. It gives accurate areas that are easy to edit. Adjust the font size & colour (from the default red) and enjoy lovely transparent fills that AutoCAD or Revit can't match yet...
- Revit being too damn smart. Mucking around with office areas, just trying to fit stuff in, I got fed up with Revit's constant warnings about the potential havoc I was creating. Yep, parametrics and smart objects are great but sometimes they just get in the way. The solution was to get a DWF, trace the areas in ADR and shunt them around trying other combinations. Do the best couple as design options in Revit and it's sorted!
Get Autodesk Design Review Free, you can also use it for review & mark-up!