Christoph Schied has released the source code for Q2VKPT - a Vulkan-based path tracer integrated into "the first playable game that is entirely raytraced and efficiently simulates fully dynamic lighting in real-time".
Consisting of about 12,000 lines of code that completely replace the original Quake II rendering code, it was originally prototyped in OpenGL with contributions by Johannes Hanika, Addis Dittebrandt, Tobias Zirr, and Florian Reibold.
The project is released as open source on Github and integrates the Vulkan path tracer into the Q2PRO client.
More information and downloads are available at http://brechpunkt.de/q2vkpt/.