Gimel Studio - Next-generation of the cross-platform non-destructive, node based 2D image graphics editor
Material Maker - Cross-platform, procedural texture generation tool.
GIMP - GIMP is a multiplatform photo manipulation tool.
NeoTextureEdit - NeoTextureEdit is an open source (GNU LGPL v.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.