TeX, BLAS, Vim and Emacs
Does the browser stack (HTML/CSS/JavaScript) count as software? If so, I don't see any of those going anywhere. The world wide web probably isn't going to be replaced anytime soon, and web browser fundamentals probably aren't going to change either.
Then again, programming languages and scripting languages in general seem like they'll last forever. Sites and programs may come and go, but the languages they're written in will probably be around for the long haul.
The Linux kernel. Just because it’s everywhere right now. Even in 1000 years when hardware has moved on, someone will want to virtualize/emulate some hardware that was running Linux.
MS Excel
/usr/bin/true
I would say some form of spreadsheet software will be with us for awhile.
I don't think much software will be useful even for one century because of competing implementations, changing requirements etc, but Github could be an archaeological treasure-trove one day.
Nothing lasts forever. No software, no programming languages, no operating systems. They will all pass out of use.
I see only git, vim, and emacs lasting until the end of my life.
Linux, PHP
vi / vim
I doubt it will last forever, but some things will last much longer than others, such as possibly TeX.
sqlite, definitely. It has a multitude of possible applications and you can built on top of it to make a more advanced use-case possible.
emacs
Windows XP. I still see it running ancient kiosks and machine tools.
Hello World examples.
Quicksort pseudo-code.
Pong, Tetris, Forth
cobol, obviously :)
Libc, zlib, sqlite3
75% of code in Common Lisp.
irfan view
winrar
Anything written in COBOL.
SAP will last forever.
AMI BIOS?
C
electron, chrome
spreadsheets
leftPad
I'm pretty sure Matlab will last forever. There is a healthy company backing it with technology lock in from many, many companies where programming is not their core competence.