In our server closet there was a mac mini sitting on another rack mounted server and plugged directly into a switch. IT found it, asked around and nobody knew what it was, so they unpugged it. Immediately the whole of engineering and support were basically offline.
Despite the thing looking suspicious as possible, I had set this thing up as an employee a year before. We were not allowed direct network access to our hosted prod network so as a "stop gap" I setup a SSH tunnel that listened on the mini's IP. At first we used this for access to the support web interface so it could be taken off the internet. At the time my request for a server was rejected. One by one more things got added to the list of things proxied over the device, eventually including basically all internal pages, git access, and about a dozen other random services. I finally got it moved into the server room, but not to real hardware. Once we built a DC we got peered access and the mini finally died.