Virtualization allows developers to run virtual machines (VMs) that emulate hardware and software. This reduces dependencies and creates flexible environments for testing legacy software and configurations. Common free virtualization tools include Virtual PC 2007, Virtual Server 2005 R2, Hyper-V, and VMWare Player. VMs are useful for testing installations, legacy systems, hardware consolidation, internationalization, and distributed processing. Tips include keeping host and guest systems on separate disks and disabling screen savers.