XenClient alternatives

[che]

I recently stumbled across XenClient which is a virtualisation software for laptops and desktops that starts directly at boot and allows for the simultaneous booting of multiple guest operating systems. After booting you can switch between OS's using ctrl+0-9, kind of similar to Linux virtual terminals.

Does anyone know if there are any open source equivalents to XenClient?

Links:
http://en.wikipedia.org/wiki/XenClient
http://www.citrix.com/English/ps2/produ ... ID=2300325