There is a guy named Arthur David Olson who maintains a small database of all the time zones in the world, including things like leap seconds and such. It’s used by everybody and it is updated several times a year. See here:

https://en.m.wikipedia.org/wiki/Tz_database

Paul Eggart is the primary maintainer for tzdb, and has been for the past 20 years.
Tzdb is the database that maintains all of the information about timezones, timezone changes, leap whatever’s and everything else. It’s present on just about every computer on the planet and plays an important role in making sure all of the things do time correctly.

If he gets hit by a bus, ICANN is responsible for finding someone else to maintain the list.

Sqlite is the most widely used database engine, and is primarily developed by a small handful of people.

ImageMagick is probably the most iconic example. Primarily developed by John Cristy since 1987, it’s used in a hilarious number of places for basic image operations. When a security bug was found in it a bit ago, basically every server needed to be patched because they all do something with images.

Furthermore, “RUNK” was originally made in the 1980s to take over from a program written on punch cards in the 1960s. Finally, it’s missing some important functions that the original 60s program had because "RUNK"s developer doesn’t see the purpose of those functions and refuses to add them; and no one has publically released a fork of “RUNK” that adds those functions back in, so you have to do it yourself. Thank God it’s open source.

Edit: oh yeah, and back in 2005 there was an effort to make a GUI for it, but “RUNK’s” sole developer got mad because “back in the 80s we didn’t need GUIs; command line is infinitely faster” and kept intentionally breaking support for the GUI with each bug fix, leading to the project eventually being abandoned.

left-pad was the first thing that came to mind for me

https://en.wikipedia.org/wiki/Npm_left-pad_incident

I mean, it was either Richard Stallman or Dennis Ritchie that created grep in an evening so that a buddy of his could do research on volumes of text that wouldn’t fit in the RAM of a PDP-11 (or similar machine. I’m telling this story from memory). It’s designed to do what you would do with the ancient text editor ed using the commands Global, Regular Expression, and Print. g re p. grep. Probably the most important piece of software ever written in a couple hours.

I’m surprised that no one seems to have brought up curl, which is maintained by Daniel Stenberg who is Just Some Guy™

I think this probably applies…

So Thief: The Dark Project (1999) and Thief 2: The Metal Age (2000), are a couple of classic stealth FPS games, proto-immersive-sims, and still some of my all time favorite games. They both use the Dark Engine, an in-house engine from the now defunt Looking Glass Studios, which also powered System Shock 2.

In 2010, the source code to a System Shock 2 port (for the dreamcast or ps2 iirc…) leaked online, and on 2012 someone used that code to create NewDark and TFix, patches to make these old games work on modern computers (and some bugfixes, support for HD, etc).

There are still updates regularly released for it too!

I must emphasize that these games are still sold on Steam, GOG, etc and this patch is essentially required for them to work. And these are hardly the only games like this, just the ones most personal to me. Retrogaming is built on the backs of unsung individual heroes who backwards-engineer, hack, patch, and mod their favorite games to keep them running for everyone long after the publishers have died or abandoned their work.

Based on my cheatsheet, GNU Coreutils, sed, awk, ImageMagick, exiftool, jdupes, rsync, jq, par2, parallel, tar and xz utils are examples of commands that I frequently use but whose developers I don’t believe receive any significant cashflow despite the huge benefit they provide to software developers. The last one was basically taken over in by a nation-state hacking team until the subtle backdoor for OpenSSH was found in 2024-03 by some Microsoft guy not doing his assigned job.

Sqlite isn’t quite one person, but it is a very small team and is extremely widely used. https://www.sqlite.org/mostdeployed.html

The guy that runs Rufus.

core-js (whose maintainer is also a bit picky about and probably doesn’t understand the OSS process) Phil Katz, the guy who invented .zip. To this day, every .zip file contains his initials in hexadecmial. His story is incredibly interesting.

Imagemagick.

Every website that supports avatar images and has multiple sizes of the avatars uses imagemagick.

Another one is OpenSSL.

Until very recently the whole Resident Evil modding community relied solely on a Maya 3DS script that a Chinese dude named Maliwei777 created in 2012. The community cherished that script but it got harder and harder to get the correct 3DS version to run it.

Steve Jobs and Steve Wozniak are the classic example. Jobs has some technical skill, but not a lot. He’s the “ideas guy” that all other “ideas guy” try to be. I don’t have a lot of respect for the “idea guy”; Jobs was a manipulative narcissist, and he should not be emulated.

Woz, OTOH, is an absolute genius, and one of the most genuinely nice people you’ll ever meet. Apple made him enough money that he can do whatever he wanted with his life, and what he wanted was to do cool things with computers and pull harmless pranks.

Bill Gates had Steve Ballmer and Paul Allen. That was more of a collaboration. They all had some level of technical and business skill mixed together. It wasn’t quite the complementary skillset we see with Jobs and Woz. A lot of Microsoft’s success was being in the right place at the right time to make the right deal.

Pretty much every basic terminal command for linux. Grep is the one that comes to mind.