Spine - Spine is 2D animation software designed specifically for software and game development.
Live2D Cubism - Live2D is the world's first drawing technology to enable 3D rendering of 2D images.
Synfig Studio - Just another WordPress site
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Unity 2D - Unity 2D is a powerful and feature-rich game design solution built from the ground up to fulfill every basic and advanced need of the developer.
Animaze by FaceRig - Livestream or Video Chat with custom 2d & 3d animated avatars. Add backgrounds & props with the Animaze editor. Use on Twitch, Discord, Skype, Zoom, & more