The ISO option creates an ISO image of the Cosmos output. This ISO file can be mounted and booted by most virtualization technologies. In addition a physical optical disk can be burned and used to boot physical hardware.
WMWare Workstation and VMWare Player are the preferred testing environments for Cosmos. This is because they are stable, reliable, and easily controlled by the Cosmos Visual Studio integration package. This second point provides for a seemless development and debugging process.
VMWare Workstation is not free, however VMWare Player is. VMWare Player for the typical Cosmos developer provides more than enough functionality.
VMWare Player can be downloaded here.
Bochs
PXE
Virtual PC
Hyper-V