2D IK/FK bone based animation tools are becoming more and more common in the animation world, and especially for game developers. The process of Cut Out Animation, or COA, can be a huge time saver, bringing a 3D animation process to the labour intensive 2D animation world.
Links
Spine -- https://www.gamefromscratch.com/post/2016/04/25/An-Introduction-To-Spine-A-2D-Bone-Based-Animation-System.aspx
Creature -- https://www.youtube.com/watch?v=9uBk5NJJLlo
Dragonbonez -- https://www.youtube.com/watch?v=ZjKBxgZ6zvE
Synfig -- https://www.youtube.com/watch?v=eFlv7O5w8Wc
Animate CC - https://www.youtube.com/watch?v=eZr8tOUe5Bg
