List of languages that compile to JS

CoffeeScript Family (& Friends)

• CoffeeScript Unfancy JavaScript

Family (share genes with CoffeeScript)

• Coco A CoffeeScript dialect that aims to be more radical and practical, also acts as a test bed for features that get imported in CoffeeScript.
• Parsec CoffeeScript CS based on parser combinators. The project's aim is to add static metaprogramming (i.e. macros + syntax extensibility) to Coffee Script (CS), similar to how Metalua adds such features to Lua. The resulting compiler, once merged with the official compiler, should be usable as a drop-in replacement for it.
• Contracts.coffee A dialect of CoffeeScript that adds built-in support for contracts.
• Uberscript, a CoffeeScript fork that adds type annotations which are compiled to Google closure compiler type annotation comments.
• ToffeeScript A dialect of CoffeeScript that support Asynchronous Syntax, Symbol and Regexp operator =~

Friends (philosophically related)

• JS11 JavaScript with augmented semicolon insertion, reduced punctuation, and limited sugar. Debugs line-for-line.
• Kaffeine Enhanced Syntax for JavaScript.
• Jack Making programming playful.
• move A simpler and cleaner programming language.

JavaScript Parsers and Extensions

• Narcissus Mozilla's experimental JavaScript compiler in JavaScript by Brendan Eich and others.
  • CommonJS version in DoctorJS
  • Jasy: Python port of Narcissus with some enhancements
  • PyNarcissus Narcissus's parser ported to Python (used in pyjon)
• Traceur Google's vehicle for Javascript Language Design Experimentation
• EcmaScript 5 Parser (es-lab)
• EcmaScript 5 Parser (qfox)
• reflect.js Implementation of Mozilla's (SpiderMonkey) Parser API in JavaScript
• bdParse a JavaScript LL(1) parser in JavaScript
• parse-js common lisp javascript parser
• ZeParser
• Esprima Educational (but fast) ECMAScript parser with output compatible to Mozilla Parser API

Javascript Optimizers

• Closure Compiler An optimizing compiler. Can generate a (line/col)-number mappings file.
• UglifyJS

Security enforcing JavaScript

• Caja Compiles ES5/strict to ES3 and supports object-capabilities
• ADsafe Client-side static verifier and API, making third party scripts safe.
• FBJS Facebook JavaScript, used for scripting FBML (Facebook Markup Language) gadgets.
• Jacaranda Static verifier supporting object-capabilities.
• Microsoft Web Sandbox Technology preview of securing web content through isolation.
• Gatekeeper Microsoft Research project.
• Dojo Secure Framework for building secure mashups.

Static typing

• Some of the ones listed below are also statically typed, such as mobl, GWT, JSIL, NS Basic, and Haxe.
• Dart by Google. C/Java-like syntax with optional typing.
• JavaScript++ adds pluggable type system and type inference, among other features
• SafeJS
• MileScript [commercial] A strongly-typed language similar to C# and Java, but which compiles to JS. free for non-profit, educational use.
• Mascara [commercial] Enhances JavaScript with powerful features like classes, namespaces and type-checking.
• Roy tries to meld JavaScript semantics with some features common in static functional languages
• Elm type-safe functional language that compiles to HTML, CSS, and JavaScript.

Synchronous to Asynchronous JavaScript Compilers (CPS)

• Streamline.js Uses underscore (_) to stand for callbacks. This fork preserves line numbers for debugging.
• mobl The new language for programming the mobile web.
• StratifiedJS JavaScript + structured concurrency. See also apollo on that site.
• NarrativeJS JavaScript extension with asynchronous futures and promises.
• jwacs JavaScript With Advanced Continuation Support.
• Jscex Write simple JavaScript code, execute it asynchronously by compiling to monadic form.
• TameJS adds new keywords 'twait' and 'mkevent'
• async.js Async utilities for node and the browser

JavaScript Language Extensions

• ContextJS is an implementation of Context-oriented Programming for JavaScript.
• Objective-J Shares with JavaScript the same relationship that Objective-C has with the C programming language: that of being a strict, but small, superset.
• Mochiscript Object-oriented JavaScript with syntactic sugar. Released as a Ruby gem.
• jangaroo AS3 (ActionScript) to JavaScript.
• Flapjax Event-driven, reactive evaluation.
• jLang adds object oriented syntax, namespaces, operators overriding
• Restrict Mode
• TIScript gentle extension of JavaScript

Ruby

• HotRuby Runs opcode, compiled by YARV on Ruby inside a web browser or in Flash.
• ColdRuby Compiler of Ruby 1.9 MRI bytecode, and a runtime written in JavaScript to aid in execution of Ruby code.
• rb2js Converts Ruby to JavaScript.
• RubyJS A successor to rb2js
• Red Writes like Ruby and runs like JavaScript
• Quby Used for game coding site, not open source.
• Opal Ruby to Javascript compiler.
• 8ball ruby-to-javascript source-to-source transformer

Python

• PYXC-PJ [CS friend] Python to JS. Can generate a (line/col)-number mappings file.
• Pyjamas Python to JS.
• Pyjs Python to (readable) JS.
• Skulpt Python. Client side.
• PyCow Python to MooTools JS.
• PyvaScript Python-like syntax to JavaScript.

Java/JVM

• GWT Google Web Toolkit, compiles java to javascript
• Java2Script Eclipse Java to JavaScript compiler plugin and JavaScript version of SWT
• j2js Java bytecode to JavaScript.
• Strongly-Typed Javascript (STJS) - Javascript code generator from a Java source. It is built as a Maven plugin.
• BicaJVM Javascript implementation of JVM

Scala

• scalagwt enhanced GWT (accepts jribble as well as java) plus scala to jribble.

C#, .NET

• jsc [experimental] Recompile your .NET assembly to JavaScript, ActionScript, PHP or Java.
• JSIL MSIL (.NET bytecode) to Javascript
• Script# [commercial] Compiles C# to JS.
• Prefix in development

Lisp, Scheme

• BiwaScheme Scheme(R6RS) in JavaScript
• ClojureScript Clojure to JS, the official version. Supports the majority of Clojure including persistent datastructures.
• clojurejs Subset of Clojure to JS.
• EdgeLisp A Lisp in the tradition of Common Lisp
• Fargo Scheme in JavaScript
• Moby Scheme A Scheme running in JS.
• nconc scheme interpreter in javascript with stack-friendly tail calls and full call/cc
• Parenscript Subset of Common Lisp to JS.
• Ralph Lisp-1 dialect that compiles to JavaScript, inspired by Dylan
• scheme2js Scheme to JavaScript.
• Scriptjure Library for generating JavaScript from Clojure forms.
• Sibilant JavaScript with a lisp.
• Spock A Scheme to JavaScript compiler that uses Henry Baker's Cheney-on-the-MTA compilation strategy
• Whalesong Racket to JS compiler

OCaml

• Ocamljs OCaml to JS.
• O'Browser OCaml bytecode interpreter in JS.
• Js_of_ocaml OCaml bytecode to JS compiler.

Haskell

• ghcjs Compile normal Haskell into JS
• jmacro Quasi-Quoted JS that you can insert Haskell values into, also supports a more haskellish version of javascript.

The rest of these probably don't work, particularly with code written for the common GHC compiler.

• https://github.com/aculich/lambdascript Compile a subset of Haskell into JS
• UHC (Utrecht Haskell Compiler) backend converts UHC core to JavaScript, allowing the compiling of Haskell code to JS.
• YHC (York Haskell Compiler) backend, as above but with YHC core language.
• jshaskell

Smalltalk

• Amber - formerly known as Jtalk
• Clamato a Smalltalk dialect that is designed to operate within the JavaScript runtime.
• Silver Smalltalk [commercial] Smalltalk in the browser.
• Lively Kernel - smalltalk/squeak-like development environment in the browser. See also Avocado, built on top of it.

C/C++

• Emscripten LLVM to JavaScript compiler. LLVM is "an aggressive open-source compiler for C and C++," as well as other languages.
• mala vala (gobject) to javascript
• Clue C language compiler to different runtimes (Lua, JS, Perl 5, C, Java, CL).

Basic

• NS Basic/App Studio [commercial] Visual Basic-style BASIC to JavaScript compiler. Includes IDE. Targets iOS and Android.
• qb.js An implementation of QBASIC in Javascript

Multitarget

• Haxe compiles to several platforms (C++, Flash, JS, Neko, PHP).
• Fantom Evolutionary object-oriented language emphasizing succinct and effective APIs (JVM, CLR, JS).
• LZX (Laszlo XML) LZX is OpenLaszlo's declarative user interface language, which is compiled into JavaScript 2 as an intermediary format, and further compiled into either JavaScript 1.5 or ActionScript 3.
• Clue and jsc above target multiple runtimes in addition to javascript

Tierless languages (produce both client & server)

• Fun A programming language for realtime webapps - compiles to client-side and server-side JS.
• Ur In the tradition of ML and Haskell.
• WebSharper Lets you compile F# to JS.
• mobl The new language for programming the mobile web.
• E Compiles E to JS. E is a secure distributed persistent pure object language.
• Sugar new programming language designed to replace JavaScript for client-side (and server-side) web development
• Opa (in private beta) write your complete application in just one language, and the compiler will transform it into a self-sufficient executable

Visual programming tools

• Waterbear
• JsMorphic - demo - also called Snap!
• ScriptBlocks
• Illumination [Commercial] Visual, cross-platform tool creates apps for Android, iPhone, iPad, Desktops and HTML5 or Flash websites. The I language underlies the tool.

Others

• Oia A port of Io to JavaScript.
• Quixe a Glulx VM interpreter written in Javascript
• Gnusto a Z-Machine VM interpreter written in Javascript
• Logo Interpreter
• p2js perl to javascript converter
• Reb2Static Rebol to Javascript
• RPN Interpreter for a language with a Reverse Polish Notation syntax.
• phype run PHP code directly in your browser
• OP4JS object pascal for javascript, in development
• jsForth
• wForth
• Pit F# to Javascript compiler
• Agda a dependently typed functional programming language and mechanized proof assistant
• SMLtoJs SML to Javascript compiler

Tools for Compiler Writers

Javascript Parser Generators

• jison Bison in javascript, used by Coffeescript
• OMeta/JS (source) metacompiler for many languages to many targets, including js.
• PEG.js parser generator for JavaScript based on the parsing expression grammar formalism
• languagejs - PEG parser written in JavaScript with first class errors
• Canopy Self-hosting PEG parser compiler for JavaScript, influenced by Ruby parser generators such as Treetop and Citrus. Depends on JS.Class library
• JS/CC LALR(1) parser generator
• jsparse PEG by Grandmaster Chris Double
• ReParse parser combinator library for Javascript like Haskell's Parsec
• p4js Monadic parser library for JavaScript
• JSGLR Scannerless, Generalized Left-to-right Rightmost (SGLR) derivation parser for JavaScript
• antlr has a javascript target
• Cruiser.Parse LL(k) parser

Javascript AST, Semantics

• Closure Compiler AST Documentation
• Spidermonkey Parser API - see also reflect.js above
• JsonML AST format used by the es5 parser
• treehugger Javascript AST transformation tools
• JavaScript Shaper JavaScript syntax tree shaping
• burrito & js-traverse - see this post for more info, as well as node-stackedy for an example and node-browserify for running it in a browser instead of node
• javascript types - lambdajs, flow typing
• SourceMap map javascript debugger output to original source
• Zeon A static visual JavaScript analyzer / editor. See also ZeParser.

See Also

• altJS a Google group and #altjs IRC channel for those interested in alternative languages for javascript ('transpilers'). There is a Try altJS feature, too, to test out various compilers in the browser.
• jswiki another github wiki with listings of various javascript libraries