We had an internal IRC (this was before Slack) and nobody thought about it. One day it went down, and traceroute had indicated it was in our server room; after checking every single server we could not find it, until someone noticed an ethernet cable that went through a run into the floor but didn't come back out. After opening the suspended floor we noticed a laptop running Solaris. That was our IRCd and the OS had an uptime of close to 8 years.