This is FNA3D, the 3D graphics library for FNA.

FNA3D was written to be used for FNA's Graphics namespace. It carries the same
API design as XNA 4.0, with various implementations available at runtime
(including Vulkan, OpenGL, Metal, and Direct3D). For shaders, we support
Direct3D 9 Effect Framework binaries via MojoShader.

Note that while FNA is the main consumer of FNA3D, we do NOT provide separate C#
bindings. If you want to use FNA3D in C#, simply use FNA instead; it's the same
API and can be used entirely by itself without dragging in other dependencies.