20 year old PC apps only work by the good graces and Herculean efforts of Microsoft. Certainly any Mac app would have died many times over if unmaintained over that time, to say nothing of all the dead OSes. But web apps from that era still tend to work in modern browsers.

I ran a fairly niche website for a while, starting around 2006. It was pretty terribly designed (eg I learned sql and javascript from working on this project), used the whole kitchen sink of css/html/javascript circa 2006, and still, it never stopped working.

The site is actually older than that -- it started around 2004 I think.

So even poorly written web apps have longevity sometimes, even when you don't intentionally design for logevity.

So, the oldest code I wrote that's still running is a bunch of web stuff.

The platform has been stable for a while now. 20 year old web pages still render just fine. Its exceptionally backward compatible.

Web apps being "done/not-done" is a different question altogether, and it depends on the ever-changing goals of the app/business behind it.

Doe 20 year old web apps using java applets or framesets and Netscape 4 DOM still render just fine?

If you have a browser with a Java plugin, then yes.

Unfortunately I don't have a Shockwave plugin, so no games for me.