In the very early 1990s, something like "Insert disk 1 and click the disk icon, then click <name of application>". Installation to the hard disk was optional, and might be one or two steps.

Later in the 1990s, installation was pressing "Next", "Next", "Next" after inserting the CD.

Perhaps not thinking of a "time when", perhaps thinking of an OS that required an IT certificate.

Because even early Macintosh System Software (classic Mac OS before OS X) was bewildering to Windows users, since any user could "drag" a program from a floppy disk onto their hard disk, leave it anywhere, and it worked.

Arguably, OS X introduced the Applications folder in 2001 partly to give people a place to drag things to and feel more comfortable that's where they could find their "Program Files" (but mostly so multi-user system users would get to add and re-use apps in a common clear place they "should" be).

But you still didn't need an IT admin.

Installing software means clicking the button, waiting, clicking yes on some permission prompts, and logging in with Google.

The only thing about any other software I can think of, that would be inherently any harder, is if it involves domain names and certificates. Which is a problem we should be working to solve, and I'm still annoyed at Mozilla for cancelling FlyWeb.

Unless you're such a big company you can definitely afford IT staff, you're probably not doing anything that needs separate services or a database or anything beyond one executable with SQLite, same as consumer apps.

Mac OS X Server?

The vast vast majority of SaaS products talked about on HN are probably not even 1/10th as complex.