[munificent]

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.

[hota_mazi]

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.

[platinumrad]

"at least one of three"

[realusername]

> 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.

[jay_kyburz]

Python already won before ML was a thing.

[realusername]

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.

[pjmlp]

It was called Zope.

[wild_preference]

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.

[pjmlp]

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

[flukus]

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