Sculptura is described as 'With an advanced clay engine and artist-tested tools, Sculptura is the most intuitive and powerful 3D sculpting app ever designed for your iPad. Sculpt engaging characters, ghastly monsters, or even intriguing abstract art anywhere you are'. There are more than 10 alternatives to Sculptura for a variety of platforms, including Windows, Mac, Linux, iPhone and PortableApps.com. The best alternative is Blender, which is both free and Open Source. Other great apps like Sculptura are Wings 3D (Free, Open Source), Autodesk Maya (Paid), ZBrush (Paid) and Autodesk 3ds Max (Paid).
Wings 3D is a subdivision modeler inspired by Nendo and Mirai from Izware. It is possible to assign materials, vertex color, UV coordinates and textures, but there will be improvements in those features before Wings goes 1.0.
Rhino can create, edit, analyze, document, render, animate, and translate NURBS* curves, surfaces, and solids, point clouds, and polygon meshes. There are no limits on complexity, degree, or size beyond those of your hardware.