DragonBones has a skeletal animation design panel named "DragonBonesDesignPanel" and a 2D skeletal animation library based on ActionScript.This app doesn't have any features at the moment.
DragonBones vs Spine opinions
It has a pretty similar UI and feature set. It can also export projects as Spine files to be used in your games (unfortunately it exports Spine data only as .json files and not as binary .skel, but it's still pretty nice).
Synfig is a free and open-source, industrial-strength, vector-based 2D animation app designed for producing feature-film animations. It eliminates the need to create animations frame by frame. It is available for Windows, Linux, and macOS.
Synfig Studio vs Spine opinions
Synfig isn't bone-based 2D animation
you can't get it into games and it isn't a runtime
You can't make game animations in Synfig Studio, only animation clips and animation movies
Enve is a free and open-source 2D animation app. It can create both vector and raster animations and even use sound and video files. It has been created with flexibility and expandability in mind.