Researchers at Imperial College London have applied machine learning techniques to reduce rendering times of standard Monte Carlo Raytracing that is used by almost all the industry leading renderers.
For most scenes, it was effective at removing fireflies and noise distortion from images that has been rendered for 1/20th of the sample amount as the final result. Effectively reducing render times by 95%.
This technology has recently been released as a web application that is free to use forever at airenderer.com