Illume is a GPU-accelerated physically based pathtracer written in C++ and CUDA. The source code is available on GitHub. Here are some of my favorite renders:
A coffee maker. Scene from Benedikt Bitterli's rendering resources.
Something is slightly messed up in my scene loading.
Recreation of the sample image on the Wikipedia
page for "Ray tracing (graphics)". 
Lucy from the Stanford 3D
scanning repository with a rough glass material. 
A textured scene inspired by one of Peter Kutz's blog
posts. 
An orange jade dragon showcasing subsurface scattering. 
All materials supported by illume. I particularly like the detail in
the glass sphere. 
Rough gold and copper. Rough conductors use a complex-valued
refractive index. 
The classic Cornell box. 