Material Maker - Cross-platform, procedural texture generation tool.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Substance Designer - Substance Designer is a node-based non-destructive application for material authoring.
Invision - Prototyping and collaboration for design teams
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
Sketch - Professional digital design for Mac.