What are some alternatives?
When comparing Aartform Curvy 3D and Substance Designer, you can also consider the following products
PathEngine - PathEngine is a middleware toolkit for the implementation of intelligent agent movement, built around and implementation of points-of-visibility pathfinding on 3D ground surfaces.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
SelfCAD - SelfCAD is an online 3D modeling and slicing software.
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.
MilkShape 3D - The MilkShape 3D website has been down for almost one week.
ZBrush - ZBrush is a digital sculpting and painting software solution.