If you want a solution that "just works", is simple to manage and can even extend to public cloud infrastructure when needed I can really, really recommend Nutanix. Migrating from VMWare is also really simple, they have a tool which makes that very easy. Do note that they use a heavily modified KVM as hypervisor.
* DIY w/ KVM/Xen
* DIY w/ OpenStack - https://www.openstack.org/
* ProxMox - https://www.proxmox.com/en/
* Paid OpenStack through one of their partners - https://www.openstack.org/marketplace/consulting/
* OpenNebula - https://opennebula.io/
* Nutanix - https://www.nutanix.com/
If you want a solution that "just works", is simple to manage and can even extend to public cloud infrastructure when needed I can really, really recommend Nutanix. Migrating from VMWare is also really simple, they have a tool which makes that very easy. Do note that they use a heavily modified KVM as hypervisor.