While I realize that Flash is no longer in vogue these days, ActionScript 3 is a really nice language and I'm surprised nobody else has mentioned it. It provide

While I realize that Flash is no longer in vogue these days, ActionScript 3 is a really nice language and I'm surprised nobody else has mentioned it. It provides things like optional static typing for speed improvements, code clarity, and improved tooling/refactoring, as well as classes and packages for organizing larger code bases. It's more of what Brendan Eich envisioned JavaScript 2 to be. That said, Apple is making it really hard for developers to choose it for all but intranet apps (for which it's really well suited). I second GWT and the responses here have prompted me to look into CoffeeScript, so thanks for asking this!