Blender for Architectural concept design
Besides an excellent artist tool, Blender is an excellent design tool. The ease of poly modeling, combined with the power of modifiers provides a flexible 3 dimensional sketch tool. As an architect and a Blender user for over 10 years, I use Blender on a daily basis in my office, HOK in London, where we deal with large scale projects and competitions. Over my time I have found Blender to be an excellent tool to iterate design ideas, as it sits comfortably between explicit modeling (e.g. Rhino, Sketchup, Autocad) and procedural/parametric modeling with longer setup times (Grasshopper for Rhino).