Spine vs GrafX2

Spine provides integrated modules for 14 major engines including GameMaker Studio, Cocos2Dx, LOVE, MonoGame, Unity, XNA, Flash, HTML 5, libgdx, Corona, and more. Generic runtime libraries are also available for C, C++, Objective C, C#, JavaScript, Lua and ActionScript 3. Dozens of third party libraries support additional targets.

No-nonsense workflow allows you to create your artwork in programs much better suited for the task like Illustrator and Inkscape for example, while Spine itself focuses only on the important task of skeletal animation.

Spine's developers provide scripts which makes exporting artwork from third party programs much easier to do.

Esoteric Software maintains public Waffle issue trackers to help plan and prioritize feature additions.

Spine received resounding support from Kickstarter backers, beating its pledge goal by over 5 times. A second successful Kickstarter added meshes and other important features.

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.

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.

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.

GraphX2 being based on older 256 bitmap software has inherited some tricks that modern pixel editors do not have . One of them being the ability to cycle color palette and produce animations and effects with it.

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.

The program has a basic support for animation using frames in newer versions. Graphics can be cloned and copied between frames and changed slightly.
See here how to animate with GrapfX2 https://www.youtube.com/watch?v=Gnq6zBZOqoM

Theme UI style can easily be changed from settings including buttons and colors.

The program is able to enforce the pixel constraints of old machines (C64, ZX Spectrum, Apple II, Game Boy Color, etc.)
For example, in ZX Spectrum mode, only 2 different colors can be used in a 8x8 pixel block.