Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Sculptura - 3D sculpting for everyone
Sculptris - Sculptris: Enter a world of digital art without barriers.
Nomad Sculpt - Nomad is a sculpting & painting mobile app, available on Android and iOS.
ZBrush - ZBrush is a digital sculpting and painting software solution.
PaintCube - Web-based 3D painting software