You can install many virtualization technologies like KVM, XEN, OpenVZ, VMware EXSi on the dedicated server to create virtual servers on it. Proxmox or Solumvm or onapp are control panel for these virtualization and which will gives you graphical interface to create,delete or manage VMs and assign additional memory, IP address, disk and etc.
We do not recommend openvz because the kernel is shared between several VPS so you wont be able to create different types( ubuntu, centos) virtual machines in one OpenVZ node.
OpenVZ is only runs on Linux. it doesn't support Windows and BSD operating systems, and custom kernels cannot be used.​