Do games count? I have a few from 1994 (Club Scud, F117A Stealth Fighter) I still play once in a while. 8) And one from 1991, Around the World is Carmon Sandiago, which I haven't played in years, but still keep for some reason.
As for actual 'productivity' app's, I still use Quill 2.2 (Apr, '94) to force open files when I'm not sure what they are, or where they came from.
As all 5 of my Macs are running OS X, I can think of only one app that would be considered "old". Once in a "blue moon", I play a little Eric's Solitaire on one of my home systems. It's a copy I've kept alive since first installing OS 7.5 in '97. I've been moving the pref file with every subsequent OS update. The count is up to approximately 15,000 games played, averaging 1 minute per game.
Speech Recognition SW, first installed somewhere around the time of Sputnik. I don't know the current version but it apparently is updated daily. What I like most about it, is the fact that it runs on virtually no memory; exactly how little is difficult to tell, but I can report that available memory is obviously shrinking with each passing moment, yet it still runs. A little buggy, but does the job. Running on an ancient chemical-electric processor, which is networked by a cumbersome and slow interface (AMP, or analogue-mechanical protocol) with a PowerMac G4.
On the G4, it must be QuickDex, a freeform database dating back to System 7.1. It's the app I got for free from my first Mac Bible CD, somewhere back before there was such a thing as a PPC Mac. Essentially similar to PhonePad, I would guess. I hacked it with ResEdit about 7 years ago so that the text entry window is resizeable to 800 pixels vertical.
I've mentioned this before, but I did run System 6's Font-DA Mover accidentally once. It launched in Classic and appeared to run perfectly. However this is of limited value (and doesn't really apply to the topic), as it has no earthly use after the introduction of System 7. Didn't crash, though.
As for games, I still play Civilisation II on the G4. It runs even better than it ever did on the first computer I used it on, a 1st generation PowerMac.
Yep, I still use WriteNow - even over my ethernet network on 9.2.2 but as MacDoc says, it be buggy! Biggest problem seems to be fairly large files - save often and early - then swithcing over to another application. Freezes royally.
Too bad, tho', because I still like the unbloated look of WriteNow and I have trouble forcing myself to launch Word.
I've successfully -- and quite happily -- made the wonderfully warm and fluid transition from 9 to X. To insert the typical 2 cents, I am far past the point of being fed up with AW's antiquity -- though I have no doubt that 7 is coming, however slowly...
OmniGraffle is the single best application on any platform!! Buy it!! Kill for it!! Step over your own mother to get a copy!!
[Note: Podboy does not advocate violence in the course of procuring OmniGraffle. YOU try to explain that after I just said what I did.]