XCP-ng or Proxmox if you need a bare metal hypervisor. Both open source, powerful, mature, and have large communities with lots of helpful documentation.
I think you can migrate ESXi VMs directly to XCP-ng. I have moved onto it about 6 months ago and it has been solid. Steep learning curve, but really great once you get the hang of it, and enterprise grade if you need stuff like HA clustering and complex virtual networking solutions.
XCP-ng or Proxmox if you need a bare metal hypervisor. Both open source, powerful, mature, and have large communities with lots of helpful documentation.
I think you can migrate ESXi VMs directly to XCP-ng. I have moved onto it about 6 months ago and it has been solid. Steep learning curve, but really great once you get the hang of it, and enterprise grade if you need stuff like HA clustering and complex virtual networking solutions.