Is there any article that tells the difference and relationship between KVM, QEMU, libvirt, virt-manager, Xen, Proxmox etc. with their typical use cases?
Use cases: proxmox web interface exposed on your local network on a KVM Linux box that uses QEMU to manage VM’s. Proxmox will allow you to do that from the web. QEMU is great for single or small fleet of machines but should be automated for any heavy lifting. Proxmox will do that.