The best Vector Graphic alternative to Spine is Synfig Studio, which is both free and Open Source. If that doesn't work for you, our users have ranked more than 10 alternatives to Spine, but unfortunately only two of them are Vector Graphic Apps.
Open-source 2D software for creating animations with vector and bitmap artwork, advanced bone rigging, tweening, timeline editing, onion skinning, multi-layer effects, audio sync, and multi-format rendering on Windows, Linux, and macOS.
you can't get it into games and it isn't a runtime
Synfig isn't bone-based 2D animation
Create interactive SVG animations with precise keyframe and easing control, custom vector paths, shape and text editing, gradients, masks, boolean operations, blend modes, snap, grid, advanced export options including Lottie, GIF, and no JavaScript required.
Russia
Romania
EU
You can't make game animations in Synfig Studio, only animation clips and animation movies