Open source / free hypervisors for homelab?

[Haltamer]

I've got a few PCs set up to build a bit of a home lab; To do so, I'm thinking of setting up a hypervisor with clustering, for the sheer fun of it.

In the past, I've used Xenserver, but especially in the more recent versions they've become quite aggressive with the "Pay us for that bit" mentality; Has anyone tried any other hypervisors that are (Relatively) easy to configure?
I'd at least like a GUI so I'm not tossing about with the Virtualhost and not the VM's themselves all the time.

VMWare would be the obvious answer, but I don't have any licenses. That leaves bare Xen, but as above, I'd rather not spend 99% of my time twiddling with the hypervisor CLI.

Any ideas?

[Haltamer]

m1dg3 said:

Proxmox is exactly what you need - it's much quicker and easier to setup than VMWare, particularly as a cluster.

I was having a look at this last night, Think it'll probably be what I go for