TL;DR of the post, generated automatically.

Rigby2D, a free and open-source 2D skeletal animation editor, now ships a native runtime for Defold.

• What it plays: Meshes, IK, constraints, skins, tint, blend modes, events, layered tracks, and whole scenes with a camera and parallax.
• Platforms: The C++ runtime builds for Windows, macOS, Linux, Android, iOS and HTML5.
• Install: Add the release zip under game.project's Dependencies, then call rigby2d.new with a skeleton and atlas.
• Speed: The post says NILA, a 39-bone demo character with hair physics, poses in about 12 µs.

It's brand new, so OP is asking for bug reports.