What are some alternatives?
When comparing virt-manager and VirtualBox, you can also consider the following products
oVirt - oVirt is a virtualization management application.
Parallels - Parallels Desktop is a virtualization software for Mac users to run Windows and Linux apps on OS X.
QEMU - QEMU (short for "Quick EMUlator") is a free and open-source hosted hypervisor that...
VMware Fusion - Simple and powerful virtual machine for Mac. Mac virtualization software. Learn more about VMware Fusion and try it free today.
Proxmox Virtual Environment - Proxmox VE is an open-source server virtualization platform to manage KVM virtual machines, LXC, software-defined storage and networking, HA clustering, and multiple other out-of-the-box tools on a single solution.
VMware Workstation - VMware Workstation is a multiple operating system handler to easily evaluate the any other type of new operating systems.