I am currently trying to figure out which solution would be best for software renting service (with proper licensing and stuff). I know its kinda stupid and so on, but I just have to develop it. Long story short - user can connect to a virtual machine (with windows guest os) using vnc and use some specific software for some specific time (eg., 1 hour). I have already considered VirtualBox, Xen and some other, but maybe somebody has a better idea. Thanks.