Ranked in these QuestionsQuestion Ranking
Pro Scriptable using Lua
GrafX2 is scriptable using the Lua language, which can be used to automate tasks and add new functionality to it. The script library features advanced color reduction and enhancement tools, palette analysis, and much more.
Pro Free, open source, and cross-platform
GrafX2 is totally free to use, copy, and modify. It's available on Windows, Linux, Mac OS X, Haiku, AROS, MorphOS, SkyOS, Syllable, Mint, and a few more systems. Basically anything is supported by the SDL library.
Pro Supports many file formats
GrafX2 supports many file formats, including the popular gif and png, but also importing and exporting from deluxe paint, degas elite, and various other editors using custom formats.
Pro Has a great palette tool
You can create gradients from one color to another, work in either RGB or HSL color space, save and load palettes, sort and organize palettes, and even work on "color cycling" images.
Pro Very large number of tools and effects
Pro Supports animations
Pro Supports tileset addition and extraction
Pro Has a customizable UI with themes support
Con Ancient interface
The interface looks and feels like it came out of a 20 year old commodore amiga.