Proxmox OpenVE looks the closest to a VMCenter/VMSphere alternative based purely on Linux (Debian to be more precise). You can add pure virtualized environments a la VMware guests, or run container based Linux(-only) guests. It comes with a cluster option with live migration possibilities.


Two disadvantages on first sight :

1. It's 64bit only


2. It comes only in the form of an appliance-based installation (which will wipe your /dev/sda)

Apart from that, very promising.