Free Texture Packer - Free Texture Packer is an open source tool that allows you to pack multiple images into one atlas for you games or sites.
Material Maker - Cross-platform, procedural texture generation tool.
Sprite Sheet Packer - Sprite Sheet Packer is online that you can easily use to pack sprite sheets, including data formats for CSS, LESS, and Phaser.
Substance Designer - Substance Designer is a node-based non-destructive application for material authoring.
Sprite Monkey - Small and fast but still full-featured sprite sheet editor.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.