Top Alternatives to Citrix XenServer

VirtulaBox is an open source software to run virtual systems on top of a physical system. Virtual systems are normally used for providing separate environment for each client sharing a single physical system.

Xen Project is a hypervisor using a microkernel design, providing services that allow multiple computer operating systems to execute on the same computer hardware concurrently.

VMware vSphere Hypervisor is a free, bare-metal hypervisor from VMware that allows users to virtualize their servers and consolidate applications.

Kernel-based Virtual Machine (KVM) is a virtualization infrastructure for the Linux kernel that turns it into a hypervisor. It was merged into the Linux kernel mainline in kernel version 2.6.20.

Proxmox VE is an open-source server virtualization management solution based on KVM and Linux Containers (LXC).

Microsoft Hyper-V Server is a stand-alone hyper-visor based virtualization product which includes live migration.

clearVM is a private cloud management solution.

Paperspace is a GPU cloud computing platform for individuals, startups, and enterprise.

Bochs (box) is a portable IA-32 and x86-64 IBM PC compatible emulator and debugger mostly written in C++ and distributed as free software under the GNU Lesser General Public License.

oVirt is free, open-source virtualization management platform.

unRAID Server is a partition management software.