Unity - The multiplatform game creation tools for everyone.
Sculptura - 3D sculpting for everyone
Godot Engine - Feature-packed 2D and 3D open source game engine.
Nomad Sculpt - Nomad is a sculpting & painting mobile app, available on Android and iOS.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
PaintCube - Web-based 3D painting software