Babel!

CoffeeScript is a little language that compiles into JavaScript. Underneath all those awkward braces and semicolons, JavaScript has always had a gorgeous object model at its heart. CoffeeScript is an attempt to expose the good parts of JavaScript in a simple way. You can use any existing JavaScript library seamlessly from CoffeeScript (and vice-versa).

Now acquired by MICROSOFT. TypeScript is a language for application-scale JavaScript development. It is a typed superset of JavaScript that compiles to plain JavaScript in any browser, any host, any OS and it is Open Source.

Statically typed programming language targeting the JVM and JavaScript 100% interoperable with Java™

LiveScript is a language which compiles down to JavaScript. It is a fork of Coco which is in turn derived from CoffeeScript. Like those two it has a relatively straightforward mapping to JavaScript. LiveScript is Coco but much more compatible with CoffeeScript, more functional, and more feature rich. LiveScript aims for increased expressiveness and code beauty.

Bublé is an ES2015 compiler. It takes your ES2015 JavaScript code and turns it into code that can run in today's environments, including old versions of Node.js and Internet Explorer.

Kaffeine is a set of extensions to the Javascript syntax that attempt to make it nicer to use. It compiles directly into javascript that is very similar, readable and line for line equivalent to the input (you can beautify if you like).

Script# brings the power and productivity of C# and .NET tools to Ajax development by compiling C# source code into regular JavaScript.

RapydScript is a pre-compiler for JavaScript, similar to CoffeeScript, but with cleaner, more readable syntax. The syntax is very similar to Python, but allows JavaScript as well. It's not another Python-in-a-browser clone, it's actually JavaScript with more Pythonic syntax.

Objective-J is a programming language developed as part of the Cappuccino web development framework. Its syntax is nearly identical to the Objective-C syntax and it shares with JavaScript the same relationship that Objective-C has with the C programming language: that of being a strict, but small, superset; adding traditional inheritance and Smalltalk/Objective-C style dynamic dispatch. Pure JavaScript, being a prototype-based language, already has a notion of object orientation and inheritance, but Objective-J adds the use of class-based programming to JavaScript.Programs written in Objective-J need to be preprocessed before being run by a web browser's JavaScript virtual machine. This step can occur in the web browser at runtime or by a compiler which translates Objective-J programs into pure JavaScript code. The Objective-J compiler is written in JavaScript; consequently, deploying Objective-J programs does not require a web browser plug-in. Objective-J can be compiled and run on NodeJS.ApplicationsThe first widely known use of Objective-J was in the Cappuccino-based web application 280 Slides, which was developed by 280 North itself. Even though Objective-J can be used (and has been designed) independently from the Cappuccino framework, Objective-J has primarily been invented to support web development in Cappuccino. »