It isn't specific to any GPU backend (OpenGL/Vulkan/Metal/DX/whatever), but supplies API-agnostic data and shader support so you can connect it to any GPU API, render engine, game engine, scenegraph, toolkit, whatever.
A demo using OpenGL is included in the core repository to show how it's done.
A sister project, osgSlug, integrates Sulghorn support into OpenSceneGraph.
Further support for Vulkan, DX, Metal, VulkanSceneGraph, Unity, Unreal, WebGPU (Webasm) etc are all possible, but we wanted to get something out there where it stands now and see what people want to make of/with it.
Everything so far has been self-funded, pro-bono by my company, AlphaPixel software development, and given away, without restrictions or holdbacks, under the MIT license.