DragonBones

It started life as a Flash extension, since that was where animators already drew their characters, letting them hang the parts on a skeleton and export motion as data rather than finished frames. Beijing-based Egret Technology took over development and built the standalone DragonBones Pro editor, with mesh deformation and bone weights.

Output is JSON plus a texture atlas, with open-source runtimes for Cocos2d-x, Unity and web engines among others. That made it popular in Asian mobile games, where Spine's per-developer licence felt like an unnecessary expense. When Flash died, the legacy was plain: the export format survived, the platform it was born on did not.