Since we're on the subject of Play, I'm going to add Akka to this list. In my experience, programming for concurrency (and even distributed concurrency) is just way more enjoyable using Akka.

I'd never heard of Japid before. Thanks for pointing it out.

That said, using a backtick character like that seems like a really error prone approach. Definitely not my cup of tea.

That's what I thought as well when I first saw the backtick, but after using it for a while I found it to be perfect.

It's rarely used in any other context (besides Lisp). It's really unobtrude, making the rest of the code standing out. It's at an easy to remember place at the keyboard. The parser is good enough to catch any quote or backquote mistakes. It's really an non-issue and you forget about it after a while.

A sample,

    <ul>
    `    for (a : list)
             <li>$a  
    `
    </ul>