"Shadow IT" is the official name for circumstances that lead to this and it's the consequence of:

A) Deprioritising "non-urgent" but "important" tasks consistently

and

B) IT being bureaucratic and/or unable to allocate budget

I had a Mac Pro (trashcan) at Ubisoft that was the only way people were able to play our studios live game from within the office. (Ubisoft had a "NO OUTBOUND CONNECTIONS TO INTERNET" policy for Studios)

That same Mac Pro was running our internal slack bot to run Maintenances (and, insult people).

I left Ubisoft 5 years ago, as far as I know that Mac Pro is still plugged in on my former desk chugging along, last time I asked my former manager about it was last year.

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At another company (now owned by Oracle), 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.