[mehrdadn]

I don't know what Yarn is, but Ray is a distributed heterogeneous computing framework. It's meant to make it easy to take fairly arbitrary computational programs (with machine learning being an important test/use case) and run/debug them in parallel across lots of machines with high performance in a natural fashion and without drastic changes. [1] The advantage compared to (say) Hadoop is that it allows for heterogeneous programming models and isn't limited to or designed for (say) MapReduce; you can invoke functions in parallel in a dynamic fashion pretty easily.

[1] You can get an idea of that here: https://ray.readthedocs.io/en/latest/