DHH's personal replacement for k8s for 37signals' apps.
MRSK seeks to bring the advance in ergonomics pioneered by these commercial offerings (ed: GKE, EKS, fly.io etc) to deploying web apps anywhere. Whether that's low-cost cloud options without the managed-service markup from the likes of Digital Ocean, Hetzner, OVH, etc, or it's your own colocated bare metal. To MRSK, it's all the same. Feed the config file a list of IP addresses with vanilla Ubuntu servers that have seen no prep beyond an added SSH key, and you'll be running in literally minutes.
blog post here with news.yc comments here. tptacek is in the comments making the pro-mrsk argument.