Proxmox VE, short for Proxmox Virtual Environment, is a hypervisor from the Austrian company Proxmox. It is open source, so it can be installed and run without a licence fee, and the company sells subscription plans that add support.
An Austrian vendor and an open code base make Proxmox VE a European alternative to American virtualisation platforms, and because it runs on your own hardware the data never leaves your premises. It suits system administrators, hosting companies and home lab users.