Maybe tar? First version is from 1979.<p><a href="https://en.wikipedia.org/wiki/Tar_(computing)" rel="nofollow">https://en.wikipedia.org/wiki/Tar_(computing)</a><p>Although mine was written in 2010.<p><pre><code> % tar --version
bsdtar 2.8.3 - libarchive 2.8.3
</code></pre>
Edit:
Actually it's probably telnet which I use to get into lab equipment. First version is from 1973. The version I run was written in 1993.
I'm guessing that some of the included BSD tools on my Mac are pretty old, because they're so simple. <a href="https://gist.github.com/pete/665971" rel="nofollow">https://gist.github.com/pete/665971</a>
Does using a recent version of something that's been updated for a while count? Adobe Illustrator's first release was March 1987, making it 32 years old this month; I use it pretty much daily. I'm currently using last year's version.<p>If not then I think it's Neko. <a href="http://splook.com/Software/Neko.html" rel="nofollow">http://splook.com/Software/Neko.html</a><p>Lately my Mac has been warning me that Neko will stop working soon once Apple drops support for 32-bit apps and that will be a sad day indeed.
Warning: nerd at work. The question may be ambiguous. To highlight: compare "what's the oldest software you still use today" to "what's the oldest software you use today". The first one refers to software you have been using over a longish(?) period and the second to software that may be old that you are using even though you may have only begun using it. I hope my pedantry (pedanticism?) isn't too inane...
Command line: basic Unix utilities (cd, anyone?)<p>GUI, used regularly: BBEdit, 1992<p>GUI, used infrequently: MS Word, 1983<p>GUI, not updated in forever: abandonware games played in DosBox
I have been using the same web browser, in terms of codebase, ideology and heritage, for over a quarter century now.<p>NCSA Mosaic -> Netscape 2, 3, 4/4.78, 6 -> Firebird -> Firefox -> Waterfox.<p>I have run other web browsers such as Opera and Vivaldi, but my main browser has always been and will always be a Mozilla product.
I still use xv by John Bradley regularly.. the most recent version 3.10a was released on 29/12/1994 !<p><a href="https://en.wikipedia.org/wiki/Xv_(software)" rel="nofollow">https://en.wikipedia.org/wiki/Xv_(software)</a>
My father, a chemistry professor, still uses PegasusMail which has been around since approx the year 1990. He is also good at handling his mail through `pine` program over a terminal.
I still use Reaktor by Native Instruments. It's been on the market since like '96 or something and it's ugly and clumsy as hell but it still sounds way better than anything else...