There are two unofficial Spine runtimes for Haxe, NMESpine and spinehx. Unfortunately, they're both pretty out of date at this point. Instead of trying to catch them up, I created a new one, using the current official AS3/libgdx runtimes as a reference:

https://github.com/bendmorris/spinehaxe

Spinehaxe is pure Haxe and isn't dependent on any external libraries.

I also have a renderer for OpenFL/HaxePunk, which includes a HaxePunk Graphic that renders animations and tracks hitboxes of slots:

https://github.com/bendmorris/SpinePunk

Feel free to use or contribute!

Sure, just replaced the old license with the Spine runtime license.