Spine, 2D Skeletal Animation For Games With Linux Support
Look what I found at the bottom of my todo list, oops! Spine is a full-featured 2D skeletal animation for games with Linux support as standard. It was successfully crowdfunded in February of 2013, so it's good to see it is alive and well!
If creation animations is your thing then this could be the software you have been needing!
They even provide the source code for all of the runtimes that they officially support, these are placed onto github for easy access.
They have a decent list of officially supported runtimes too including Unity, LOVE and plenty more, they even list third party runtimes too, see them here. I think toolkits like Leadwerks and Godot may want to speak to these guys to get some support too!
So, that's one less roadblock for developers working directly on Linux, next!