I think you need at least one of three things to get a new language off the ground:

1. Extreme compatibility with the current entrenched language so you can incrementally migrate. C++ from C. CoffeeScript and TypeScript from JavaScript. Kotlin from Java.

2. A killer app (well, framework). Rails for Ruby. WinForms for C#. Applets and J2EE for Java (later Android).

3. A new platform where you must use the language to target it. C for UNIX. Objective-C for iOS. JavaScript for the browser.

There are a few exceptions here and there, but the above are the typical well-trod paths to success for a language.

I listed two clear counter examples to claim #2, C++ and Javascript. I'm even tempted to put C in that list, because C was already popular before Linux.

What was Python's killer app?

What is Rust's killer app?

Go's?

Kotlin's?

Java is a counter example to your claim #3 since it not only does it run on all OS'es but you can also develop it on all OS'es.

"at least one of three"

> What was Python's killer app?

Not a killer app, but the fact you have so many ML frameworks

> What is Rust's killer app?

That's clearly Servo.

> Go?

It was docker which really made Go take off, it was their first big platform.

> Kotlin's?

Android compatibility, before that it was a niche language not being picked up much.

Python already won before ML was a thing.

In his early days, Python did not need anything, it was simply nicer to use than the other languages. Nowadays ML is a big plus.

It was called Zope.

Killer app is the wrong phrase. Rather every new language needs a competitive upside over existing languages to be successful. At which point your proposed questions have easy answers.

C++ and Javascript are definitely not counter examples as I commented.

Outside of the HN bubble python is the only one of those that got off the ground so far.

> C++ never had a killer app to start its momentum.

C++ was immediately adopted by all major C compiler vendors as it came from AT&T as well.

Microsoft C/C++ 7.0 for MS-DOS was the very last one to adopt C++ on the toolchain.

It was the lingua franca of all major desktop OS GUI frameworks, leaving C just for their lower layers, MS-DOS (Turbo Vision), OS/2 (C/Set++), Windows (OWL, VCL, MFC), Mac OS (PowerPlant, MacApp), BeOS, Symbian.

If you were doing plain C GUI programming you were doing it wrong.

> Neither did Javascript.

JavaScript owns the browser, there is hardly any other alternative regarding "browser systems programming".

> or Java really (or maybe applets, back in the days?).

Java's portability was a gift compared with C compilers still in the middle of migrating from K&R C to ANSI C, C++ compilers which were silos with their GUI frameworks and a standard still a couple of years away to be fully defined.

These days it's mostly about apps, because apps are the main thing that facilitate the transfer of $$$. In the 80s and 90s, enterprises were full of $$$ and needed fast and safe languages for writing all their software. C++ came out to solve this need, and Java came out saying it could do it better. Today enterprises are moving many of their internal tools to the web. Enterprises don't need apps per se, but they do need the tech needed to build internal apps and apps to bridge between them and their partners. Consumers are using desktops less, and mobile or web more. Apps are basically the current de facto software "product". But a lot more goes into making apps today than 30 years ago. An example is how most apps need ML for spam protection and recommendation algorithms, or they are instantly going to be considered outdated and behind the times.

>In the 80s and 90s, enterprises were full of $$$

More than today?

I haven't had my caffeine yet today cut me some slack :)

Golang and Rust also didn't have any killer app.

Rust definitely has Firefox

Just thought I'd remind you that there are currently 0 Rust jobs on Indeed.co.uk by title for the whole of the UK. The HN bubble is not how the world at large operates.

Two examples from Indeed.de in Germany, there are other results.

https://de.indeed.com/viewjob?jk=6c49a2deeb389df8&q=rust&tk=...

https://de.indeed.com/viewjob?jk=6823f26122417b2d&q=rust&tk=...

Firefox is not the kind of app to drive adoption of the language (like Rails or Python scientific libs etc). It's just an app, people using it could not care less what it's written in.

Go has Docker

Yes, but it didn't have anything before it, and yet it gained adoption like crazy.

Go has a bit of a niche, and Rust is trying real hard, but they aren't Javascript or Java, or C#, or Python, or Rails, or PHP, or C++, or Objective-C or... Out in the wider world, they are very much playing catchup, and have a very far way to go.

Javascript had the web. And, Java had the JVM. A killer 'app' is not necessarily singular & discrete.