Ask HN: Alternative container technologies for K8s in production?

I would love to hear feedback on your or others' experiences of architecting, deploying and maintaining K8s production clusters, using alternative container technologies (e.g., AWS Firecracker & Kata Containers, for micro-VMs, and containerd & Singularity, instead of Docker, for containers). Pros, cons, use cases, tooling, cloud providers support, other aspects you want to mention ...