VirtualBox -recently purchased by Sun Microsystems - supports "seamless mode" for guests, so that you can run Linux host & Windows VM, with "start" menu from both appearing on your desktop, and apps launched in separate windows. (http://www.virtualbox.org/wiki/Screenshots) ... Virtualbox host can be Lin/Win/Mac, guests can be Win/Lin (probably Mac too) as demonstrated more clearly in screenshots http://liquidat.files.wordpress.com/2007/09/virtualbox150_nahtlos_linuxhost-winxpguest21.jpg http://www.virtualbox.org/attachment/wiki/Screenshots/VirtualBox_OSX_beta_3.png Disclaimer: I do not work for, nor am I affiliated with Innotek or Sun Microsystems. »

What about KVM. ... Kernel Virtual Machine (unless I am mistaken), another linux virtualization option. my other 2 cents: OpenVZ = very quick, but not true VM, hence useage of Virtual Environment, coz it's like super-chroot. Hosts on certain distros of Linux. Gratis & Libre. Xen = supports h/ware vmx/vmt for better performance: Linux host. Gratis & Libre. VMware server = easy to set up and use. Supports hosts on Win/Lin/Mac. Gratis At the moment I mostly use OpenVZ and VMware. Provisioning tools in Xen were too painful last time I tried (end 2007). »