http://synbioproject.tech/cpi/applications/cadnano/
Cadnano simplifies and enhances the process of designing three-dimensional DNA origami nanostructures. Through its user-friendly 2D and 3D interfaces, it accelerates the creation of arbitrary designs. The embedded rules within cadnano, paired with the finite element analysis performed by CanDo, provide relative certainty of the stability of the structures. Source