Resources for Machine Learning in Ruby

I have only just started using it in a tiny experiment, so I really can't really tell more than that. On a side note GSoC rejected a project for implementing a Ruby API for the popular TensorFlow library, but initial steps are being made for privately founding it. You can see discussion here: tensorflow/tensorflow#50 (comment). Maybe it could be helpful to have this listed here too, in order to drag even more people and attention to that, given the importance of that library.