Material Maker - Cross-platform, procedural texture generation tool.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
Filter Forge - On the surface, Filter Forge is just a Photoshop plugin, a pack of filters that generate textures...
GIMP - GIMP is a multiplatform photo manipulation tool.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.