Ironically enough, none of my early "apps" still work - if you take "app" in the modern sense to mean a web or mobile application. They all rely on combinations of Perl and C and CGIs and stuff. One I found mentions that it "should" work with the new Debian 3 and Internet Explorer 6. Too much hassle to try to sort that lot out.
The earliest thing I found that was self-contained, given to the world at large, and still runs, seems to be a game of 3d naughts and crosses ("tic-tac-toe" to some of you). You can download it for DOS from ftp.funet.fi where it seems to have been uploaded sometime in 1993. This may be a time period before you were born, but fear not. We had scared away most of the dinosaurs by the late 1970s. You can play it if you use something like DOSBox
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