Phoenix is obviously “the big thing” and no other language/framework combination has something as good as LiveView. Rails cannot compete there.
Other than that, building Livebook apps for our customer success team has been really great and easy.
There’s quite a big push for ML in Elixir right now, and then there’s also Nerves for embedded programming, which I’ve never dabbled in but it looks nice.
LiveView is definitely Elixir's killer app. It's what takes Phoenix from "a really good web framework" to "the singular best web framework", in my experience. Ecto is also a best-in-class data-layer adapter (ORM seems wrong and reductive).
As someone currently using bleeding edge Blazor at work, and Phoenix on my own time, this is wromg to the point of comedy.
The big thing that LiveView has going for it is that it transforms the client session into just another process to communicate with, using the same message passing tools as the rest of the language, with very little headache because concurrency is already an expectation.
Blazor can never achieve this, because C# is not a concurrency focused language.
ecto is also just an amazing db wrapper in general. you basically write sql in elixir which means you can optimize the crap out of your queries and its easy to steop down to actual sql where needed via fragments.
There’s quite a big push for ML in Elixir right now, and then there’s also Nerves for embedded programming, which I’ve never dabbled in but it looks nice.