Proxmox Virtual Environment is a complete open source server virtualization management solution. It is based on KVM virtualization and container-based virtualization and manages virtual machines, storage, virtualized networks, and HA Clustering.
Zentyal Server offers native Microsoft® Exchange protocols implementation and Active Directory interoperability on Linux. Zentyal, based in Zaragoza (Spain) is the first company ever to offer native Microsoft® Exchange protocol implementation and Active Directory interoperability on Linux.
Ubuntu Server 14.04 is the latest LTS release of Ubuntu server. It includes OpenStack Icehouse and many new features and tools for cloud and hyperscale computing. LTS stands for Long Term Support. It means that the 14.04 release will be supported by Canonical with maintenance and security updates for five years.