Material Maker - Cross-platform, procedural texture generation tool.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Substance Designer - Substance Designer is a node-based non-destructive application for material authoring.
ZBrush - ZBrush is a digital sculpting and painting software solution.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.