Proxmox is totally free, there are a few nag prompts, but nothing that interferes with the functionality of the host. I think they have special subscriber-only repos, but I'm not sure they contain anything you can't get elsewhere.
edit: No, never tried unRAID. My host was originally intended to run Server 2016 Datacenter, with hyper-v guests. Ryzen drivers were nowhere to be found, and ESXi didn't work either. Proxmox was the first solution I found with good/full hardware support, so that's what won