you buy one or more of the data-centre-rack-sized computers, hook em up to each other / your datacentre network, and you now have essentially a cloud services platform like AWS/Azure, in your own datacentre, under your control, with full visibility of what every part of the platform is doing (hypervisor, underlying bare metal kernel, firmware, bootloader, etc), because it's ALL open source, written from the ground up by them
I think it's pretty neat!