It's a Ruby wrapper for the popular Google TensorFlow ML library. It will probably be completed before this autumn because it was originally a GSOC project (and couldn't be admitted because it was found to be missing some Google requirements at the last moment). It's now crowdfunded but it seems that Google is still offering some degree of support to interested developers [1].
In the meanwhile also check this out https://gist.github.com/gbuesing/865b814d312f46775cda "Resources for Machine Learning in Ruby", some of which are again wrappers around popular ML C libraries, thus removing the problem about sheer speed.