Ben Carter made an incredible mod for the Super Nintendo that adds real-time raytracing capabilities to the vintage console. It uses in-cart hardware similar in principle to the official 1993 Super-FX chip that was used to juice the 16-bit machine's 3D abilities. But this enhancement is much more powerful.
The idea originated when I was trying to think of an interesting idea for a project to help me learn Verilog and FPGA design, and the notion of building a simple raytracer came to mind (partly inspired by a scarily smart friend of mine who is building his own GPU). A bit later – because sometimes my brain hates me and delights in coming up with silly things to do – this turned into "wouldn't it be interesting to try making a SNES do raytracing?", and thus the SuperRT chip idea was born.