Maximum number of guests?

Hi everyone and thanks in advance for any help.

My problem is I am trying to find how many guest OSes can be installed on a host machine with this software. I looked at Microsoft but their Hyper-V only allows around 350 guests. I will be needing at least room for a thousand. I know Microsoft has a server 2008 Datacenter edition that will give me what I need but I prefer something more open source so I can make code changes as I see fit. If KVM cannot fit this bill could anyone recommend a product or two I could research?

Will all guests be running simultaneously? You’d need some serious hardware for that…

Other than that, I am not aware of restrictions within KVM.