TypeScript lets you write JavaScript the way you really want to.
TypeScript is a typed superset of JavaScript that compiles to plain JavaScript.
Any browser. Any host. Any OS. Open Source.

Get TypeScript Now  

Node.js

The command-line TypeScript compiler can be installed as a Node.js package.

Install
npm install -g typescript
Compile
tsc helloworld.ts

Tools

Visual Studio 2013 Update 2 RC includes TypeScript. Visual Studio 2012 developers can install the TypeScript editor plugin to get rich TypeScript tooling. There is also TypeScript support for other editors available.

Download for VS 2012

Get VS 2013 Update 2 RC

Open Source

TypeScript is being developed on GitHub. The TypeScript compiler is implemented in TypeScript, and can be used in any JavaScript host.

Get the source code

Contribute

Read the specification in doc or pdf

Play with the bits and file bugs.

Join the #typescript Twitter discussion and follow the GitHub project.

Learn

Tutorial - Best way to get up to speed on TypeScript.

Forums - Great place to get help with using TypeScript.

Blog - Keep up to date on the latest news.

DefinitelyTyped - Repository of library typings.