Io programming language

The PHP Interpreter

The .NET Compiler Platform ("Roslyn") provides open-source C# and Visual Basic compilers with rich code analysis APIs.

The Swift Programming Language

a Productive Parallel Programming Language

Unfancy JavaScript

D is a language with C-like syntax and static typing. It pragmatically combines efficiency, control, and modeling power, with safety and programmer productivity.

The Dart SDK, including the VM, dart2js, core libraries, and more.

Open Dylan compiler and IDE

Elixir is a dynamic, functional language designed for building scalable and maintainable applications

Erlang/OTP

The Open Edition of the F# compiler, core library and tools

Frege is a Haskell for the JVM. It brings purely functional programing to the Java platform.

The Go programming language

The Gosu programming language

Compiler for the Elm programming language. Elm aims to make web development more pleasant. Elm is a type inferred, functional reactive language that compiles to HTML, CSS, and JavaScript.

A small strongly typed language that compiles to Javascript

Haxe - The Cross-Platform Toolkit

The Clojure programming language

The Kotlin Programming Language

The Groovy programming language

Golo - a lightweight dynamic language for the JVM.

An implementation of the Smalltalk language that runs on top of the JS runtime http://amber-lang.net

Julia is a high-level, high-performance dynamic language for technical computing.
The main homepage for Julia can be found at julialang.org.

Julia programs are organized around multiple dispatch; by defining functions and overloading them for different combinations of argument types, which can also be user-defined. For a more in-depth discussion of the rationale and advantages of Julia over other systems, see the following highlights or read the introduction in the online manual.

LiveScript is a language which compiles to JavaScript. It has a straightforward mapping to JavaScript and allows you to write expressive code devoid of repetitive boilerplate. While LiveScript adds many features to assist in functional style programming, it also has many improvements for object oriented and imperative programming.

Nim (formerly known as "Nimrod") is a compiled, garbage-collected systems programming language which has an excellent productivity/performance ratio. Nim's design focuses on efficiency, expressiveness, elegance (in the order of priority). http://nim-lang.org/

The Nu programming language.

The core OCaml system: compilers, runtime system, base libraries

The Racket repository

Red is a next-generation programming language strongly inspired by Rebol, but with a broader field of usage thanks to its native-code compiler, from system programming to high-level scripting and cross-platform reactive GUI, while providing modern support for concurrency, all in a zero-install, zero-config, single 1MB file!

Ruby is the interpreted scripting language for quick and easy object-oriented programming. It has many features to process text files and to do system management tasks (as in Perl). It is simple, straight-forward, and extensible.

You can read more about ruby on its website.

A safe, concurrent, practical language.

The Scala programming language

A language for GPU computing.