Tons of choices, k8s is really just a definition of an API and there lots of things you can plug in at various points to implement parts of the API (or even completely extend it). Read the official docs--they'll walk you through the design and capabilities. As far as what's available, well it's a bit like trying to understand "what's the newest programming languge?" You probably want to plug yourself into the k8s community and start looking at subreddits, SIG meeting notes, community news, etc. New things are popping up literally every day.