Comment (Open) Solaris (Score 2, Informative) 121
Solaris 10 and Open Solaris have the concept of zones and containers. The computer runs a single Solaris instance but can run isolated process trees in zones which share common libraries but can be updated for dependencies independently. The containers concept (in conjunction with zones) allows a fair share scheduler to guarantee a service level for each allocated zone (CPU/memory sharing, etc). IMHO, must better than Virtuozzo, VMware and Xen.