Substance Designer - Substance Designer is a node-based non-destructive application for material authoring.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
PixaFlux - PixaFlux is a node based image processing application.
Material Maker - Cross-platform, procedural texture generation tool.
FilterJS - Open source, node-based procedural texture generator.
Filter Forge - On the surface, Filter Forge is just a Photoshop plugin, a pack of filters that generate textures...