XCP-ng

XCP-ng forked from Citrix Hypervisor (formerly XenServer) specifically to keep a fully open-source, community-governed version of that Xen-based virtualization platform available, free of Citrix's commercial licensing and feature restrictions. It's commonly paired with Xen Orchestra, a separate web-based management application (from the same community) for managing pools of XCP-ng hosts, VM backups, and live migration from one central dashboard. Alongside Proxmox VE (which uses KVM rather than Xen), it's one of the two leading open-source alternatives that gained significant additional attention after VMware's licensing changes under Broadcom pushed many organizations to evaluate non-VMware virtualization platforms.