Dominik Holling writes "With a small announcement on their mailing list, the open source community hypervisor Xen has reached the official release of version 4.0.0 today. The new features are: 'blktap2 (VHD support, snapshot discs, ...), Remus live checkpointing and fault tolerance, page sharing and page-to-disc for HVM guests, Transcendent memory (http://oss.oracle.com/projects/tmem/).' A complete list of all changes can be found on the Xen wiki and the source can be found on the official website and the Xen Mercurial repositories."
Trailrunner7 writes "Joanna Rutkowska, a security researcher known for her work on virtualization security and low-level rootkits, has released a new open-source operating system meant to provide isolation of the OS's components for better security. The OS, called Qubes, is based on Xen, X and Linux, and is in a basic, alpha stage right now. Qubes relies on virtualization to separate applications running on the OS and also places many of the system-level components in sandboxes to prevent them from affecting each other. 'Qubes lets the user define many security domains implemented as lightweight virtual machines (VMs), or 'AppVMs.' E.g. users can have 'personal,' 'work,' 'shopping,' 'bank,' and 'random' AppVMs and can use the applications from within those VMs just like if they were executing on the local machine, but at the same time they are well isolated from each other. Qubes supports secure copy-and-paste and file sharing between the AppVMs, of course.'"
Xen's also just reached 4.0; some details below.