I guess that the most common case is not an interactive work, but some kind of automation systems built a long time ago, that just works, eg. Amiga 2000 running school heating system [1] or C64 running driveshaft balancing calculations [2].

[1] https://www.woodtv.com/news/grand-rapids/1980s-computer-cont...

[2] http://wbj.pl/auto-garage-in-poland-uses-commodore-64-to-run...