Material Maker - Cross-platform, procedural texture generation tool.
Substance Designer - Substance Designer is a node-based non-destructive application for material authoring.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
TexGraph - Node-based, procedural texture creation tool for Windows.
Filter Forge - On the surface, Filter Forge is just a Photoshop plugin, a pack of filters that generate textures...
DarkTree - DarkTree 2.5 is an advanced procedural shader authoring tool.