> Just look at the code of GitHub, BitBucket, Sourceforge etc

I think those are misleading on two accounts: first, it's the tip of the iceberg. Most co-workers I've spoken to don't contribute to any such open source projects. They tend to have other priorities, starting with the proprietary or custom software they are paid to write. Yes, there are many programmers writing open source code out there. I'm willing to guess however that much more time is spent on proprietary or custom software.

Second, there's a lot of unused garbage out there. Yes, there are a massive amount of code that could be used by others, but the only code you see is the tiny fraction that is actually used by many people. Such is the way of search engines, they show you a highly skewed sample, biased towards fame. (And rightly so: famous stuff everybody use tends to be what you are interested in to begin with.)

> Each developer uses a bunch of libraries, utilities and frameworks which are either FOSS or could use a FOSS alternative.

That's the thing: everybody uses a bunch of libraries and utilities all the time. I believe much fewer people writes those utilities. Or at the very least, much less time is spent writing them.

The more popular the library or utility, the more pronounced this is. Everybody can write something 10 other programmers will end up using. Very few will be (un)lucky enough to write something that have enough users to be known across the planet.

Take me for instance. I've sought my GitHub ranking¹ which is mostly concentrated in a single project². Numbers suggest I'm in the top percentile. Not the most popular code out there, but I'm doing pretty damn fine.

[1]: http://git-awards.com/users/loupvaillant
[2]: https://monocypher.org

Yet: have you even heard of those? Possibly, but I'd say probably not. The top percentile simply isn't enough.

> […] you can work on somewhat-popular or even niche software which is still used by hundreds of thousands, or just thousands, of people. That's still very significant!

Agreed. This is all a matter of degree, after all.

> I think programmers worth their salt should strive to produce code that other programmers use.

I'm not sure I agree with that goal. And I say that as someone who dreams of having a global impact. Sure, any professional worth their salt should strive to improve to at least some decent standard of excellence. (Some professions, like classical music, tend to require excellence merely to enter the field, which we could argue is maybe going a bit too far.)

Having other programmers use your stuff is a great way to have feedback and improve up to that standard, but I don't think it's not the only way. It may currently be one of the easiest, though.

> I believe that it's the visible code, and the free code, is what we should use as the model and the target of advice and improvement.

If we're going down that path, I'd go as far as to say pretty much all code should be free to begin with. Following that thought to its conclusion though, I quickly concluded that universal free software is mostly incompatible with capitalism. I can write software in my free time, but I need a salary in the first place to even have such free time. Currently, that salary comes from a day job dedicated to proprietary software.

I mean, recall the OpenSSL debacle. That piece of software is used literally everywhere, and we had to have Heartbleed for insanely rich corporations over the world to even notice that trickling a few drops of money down this project might be a good idea.