GeeXLab, the successor of GLSL Hacker, comes with the support of Direct3D 12. It’s not a full support but most of the basic things are available: command lists (CL), pipeline state objects (PSO), constant buffers (CB) and HLSL shaders.
The wizard behind Shadertoy has struk once again with this beautiful demo showing an animated snail.
La Calanque is a nice demo and a heavy pixel shader test based on this Shadertoy demo. This test is perfect to benchmark high-end graphics cards.