Software Ray and Path Tracing

Peter Shirley's Raytracing in One Weekend series
Physically Based Rendering: From Theory To Implementation Matt Pharr, Wenzel Jakob, and Greg Humphreys, 3rd and 4th Edition.

DX11

DX12

A Gentle Introduction to D3D12 (2022), Alex Tardif
3D Game Engine Programming - Learning DirectX 12

DX12 Ray Tracing

Microsoft DirectX-Graphics-Samples D3D12Raytracing
Nvidia DX12 Raytracing tutorial - Part 1
Nvidia GameWorks DXRtutorials
ScrappyCocco DirectX-DXR-Tutorials

Vulkan

Khronos Vulkan Introduction
Khronos Vulkan C++ bindings for Vulkan
Vulkan Lecture Series, TU Wien, YouTube
Sascha Willems Vulkan C++ examples and demos

Vulkan Ray Tracing

NVIDIA Vulkan Ray Tracing Tutorial

Path Tracing

Christoph Peter's Shadertoy Workshop
Aras Pranckevičius' Daily Path Tracer
Daqi Lin's GPU path tracer