oneSIS is an open-source software tool developed at Sandia National Laboratories aimed at easing systems administration in large-scale, Linux cluster environments.
The official tag line for oneSIS is that it is a thin, role-based Single Image System for scalable cluster management.
Changing a node to boot into a different image only requires a quick modification to /etc/sysimage and a reboot of the target client.
Since oneSIS was designed with the Linux-systems administrator in mind, users will not find proprietary-GUI frontends here; all the tools to image a box, copying root-images, converting diskless machines diskfull, etc.
The goal is to let Linux systems administrators feel at home with the typical CLI tools they're already used to.