Some years ago a friend of mine and I built a "self-propagating" system to speed up server deployment. Every server inside the datacenter would periodically look for hardware it wasn't previously aware of in its subnet, and then it would try a few known exploits to root the box, and run our shim. The shim would install all the software we wanted on the box, apply patches, reboot the machine, bring it online and register it so that all the other machines knew about it.

It was kind of a fun experiment, but in the end didn't save us enough time to maintain it for very long - the real time sink was getting the hardware bootable and into the datacenter to begin with. (This was pre-"cloud" days, I guess if we were doing it again now we might have used it for a little longer.)