Question: I am not looking for a necessarily super-robust solution with a 10-year track record, but for something that can be used in a real applications, and goes beyond just being able to run an Hello World example.

My preference is to run the compiler on the server, so I can compile Haskell code ahead of time. Of course, the solution would need to be more than just a compiler, and enable Haskell code to access the API available on the browser (DOM, XHR…).

Footnote: the projects I have seen so far don't seem to be actively maintained, or to go beyond being able to run "Hello world", or in some case even to go beyond a project description.

Answer: 
While GHCJS does not seem to be actively maintained, [Emscripten](https://github.com/kripken/emscripten/wiki) seems to be quite current.

* Emscripten compiles [LLVM](http://en.wikipedia.org/wiki/LLVM) bitcode to JavaScript.
* [GHC's LLVM backend](http://www.haskell.org/ghc/docs/7.6.1/html/users_guide/code-generators.html) appears to be actively developed.
* Intuitively, to answer the question, the following pipeline might not be very far from "production quality": Haskell lexemes (-> GHC ->) LLVM lexemes (-> Emscripten ->) JavaScript lexemes

I'll admit that this is a speculative post.
This language, **Roy**, is perhaps not really Haskell (?), but it seems very similar:

<http://roy.brianmckenna.org/>

Roy seems to be alive; there are many forks in the GitHub repo: <https://github.com/pufuwozu/roy>  

and it seems to be alive: <https://github.com/pufuwozu/roy/graphs>

If you're using Play Framework 2.0, then there's a plugin, **Ray**, to run Roy on Play Framework 2.0:

<http://brianmckenna.org/blog/ray>  

<https://github.com/pufuwozu/ray>

The last commit was four months ago, which is rather long ago keeping in mind that Play Framework 2 was released perhaps 4 or 5 months ago.