At some point there was a Mac OS (classic Mac OS in the 90s) that displayed a hard disk activity icon to the left of the Apple menu icon. I’ve looked for the name of the utility or setting off and in for years and have been unable to find any mention of it. I seem to recall seeing it on many unrelated Macs, which made me think it was a system setting, but having gone back through several system versions I’ve never been able to find it.
Not quite the same as what TFM has made (which is awesome), but hearing the crunch of a hard drive and seeing that LED flash or the activity indicator blink are so pleasantly nostalgic.
iStat Menus offer this for modern macOS. The disk activity is not that relevant for me, but networking is useful. When I'm waiting for something and there is no network activity I know something's fishy.