Proxmox is great. I use it for experimenting with Lightwhale swarm clusters locally; I'm currently running 8 Lightwhale worker nodes with 512MB RAM each and no disk, and it's super fast and fits in my pocket.

I don't consider Lightwhale as an alternative to Proxmox. In fact, how do you even run a Docker container in Proxmox? Without booting Lightwhale in a VM first, I mean? ;)