The CentOS Project is pleased to announce the immediate availability of CentOS 7 for x86_64, including images for docker, and various cloud providers. There are many fundamental changes in this release, compared to previous releases of CentOS. Notably the inclusion of systemd, Gnome3, and a default filesystem of XFS. For more information about what makes CentOS 7 stand out, please see our release notes.
CentOS 6 can be upgraded to 7, but that functionality is still being tested.
Scientific Linux 7 alpha is also released. It does not depend on the Red Hat infrastructure, although it uses RHEL as upstream, so it is more independent than CentOS.