Spirit - The animation tool for the web.
Spine - Spine is 2D animation software designed specifically for software and game development.
Marionette Studio - Marionette Studio is an online animation software for beginners and professionals. Animate 2D characters and environments in minutes with no prior skills.
Synfig Studio - Just another WordPress site
Lottie by Airbnb - Easily add high-quality animation to any native app
AnimeEffects - AnimeEffects is a 2D keyframe animation tool based on deformation of polygon meshes.