It’s used with Flutter, Google’s app development framework. I really enjoy Dart as a language, but it is fairly young and missing a few conveniences (such as data classes). It also can’t compile to dynamic libraries, only executables. Despite that, it is very pleasant if you enjoy managed languages.

I taught myself Dart a couple of years ago, and enjoyed the language, but never found a compelling use for it.

For anything I might do in Dart, there's a better alternative. For backend stuff, I'm going to write in Java or Kotlin. For frontend stuff, I'm going to write in JS or TypeScript. I like Flutter, but Flutter by itself isn't reason enough to adopt Dart.

Long term, if Jetpack for Desktop actually takes off, I don't see any reason to write in anything but Kotlin.

I think there was a fork of Chrome that included Dart as another language runtime alongside JavaScript.

It's used in Flutter exclusively, and since Flutter is hardly used at all, it's a pretty unknown language, and will probably always remain so.

It doesn't help Dart that Kotlin and Swift have been null safe languages for a decade now.