All runtimes support all Spine editor features where the game toolkit allows it. Love and Corona currently don't render meshes. Unity has the most features (thanks to Mitch!). The runtime for Unity can interact with Unity GameObjects, eg to have parts of the skeleton driven by physics. This can be done in other runtimes, but you'll have to implement it. It isn't super hard, but in Unity you can just click the mouse around to do it.

This shows how easy it is to setup a cape to be controlled by Unity physics:
https://www.youtube.com/watch?v=RFCpqeW2FHA

This shows Spine's IK keeping feet from penetrating the ground as well as keeping the hands on the sword, plus the cape physics:
https://www.youtube.com/watch?v=_S22WIWOp7c#t=174

Here's a (very strange) Unity web demo of IK:
http://www.xdtech.net/spine/bawk.html
It was inspired by this forum post about chickens and IK:
viewtopic.php?f=8&t=2753&p=19144

Spine works with normal mapping to give realistic lighting for skeletons, taking into account bone rotation so lighting is correct for any skeleton pose. This can make skeletons look very 3D.
https://www.youtube.com/watch?v=QrlbYXKR_OA

Our Spine Unity runtime also can do "baking", where it converts a Spine skeleton into a bunch of native Unity scene graph objects, plus native animations for those objects. This allows you to use Spine for rigging and animation, then convert to Unity game objects for use with other Unity features. This video is a bit long, but shows it if you are interested:
https://www.youtube.com/watch?v=sCBnFK9PEmU

Finally, Spine skeleton animations can be used with Unity's Mecanim, which is their animation system with a state machine, blend trees, etc.

You're welcome.

Also Unity can render parts of one skeleton between parts of other skeletons, or even 3D gameobjects without pushing them further back into ZSpace using "Submesh Separators"

I don't understand this part: "taking into account bone rotation so lighting is correct for any skeleton pose.".

Do you mean that you consider that the bone is pointing the light in 2d?

If an attachment is rotated by a bone, the information about the bone's world rotation and scale are passed into the shader as components of its mesh's vertex tangents and that information is used to rotate and offset the normal map that is generating the lighting effect. Additionally, a Skinned mesh that is deformed via weights takes into account the rotation/scale of the most significant bone per vertex to calculate its corresponding tangent.

Darky escreveu

How can we read binary skeleton data? (runtime-c)

Reading binary hasn't yet been added to spine-c. You'd need to port it from spine-libgdx.

@Nate, could you please show the shader you used for this video? ->
https://www.youtube.com/watch?v=QrlbYXKR_OA

Looks really good. It's a normal light scene with the shader, nothing else?

There's also a directional light casting the shadows and providing a small over-all lighting boost (in lieu of an ambient source)
Nate doesn't have the shader.