At one place I worked we had a service that had been part of an acquired company that, as far as I could tell, had no one responsible for maintaining it, and it either zero or almost zero users, so it would go down for weeks at a time before somebody noticed and did something about it, usually because it needed a security patch. To this day I have no idea why it wasn't shut down but AFAIK it's still out there causing problems for whoever works there now.

We came up with a bunch of ways to describe its uptime: a service has one fortnine of reliability if it stays up for at least one continuous fortnight of the year, for instance. An absolute nine is nine days per year. Fractional nines were invented: a "quarter nine" was 25% of 90%uptime, or 22.5% total uptime.