Here’s a good overview of and introduction to TypeScript by Anders Hejlsberg:
Now that the parameter has a type annotation, we can also get quality IntelliSense for it. In addition to listing the members of string, the IntelliSense also lists what types the members have (and when the members are functions, this includes the types of its parameters, too):
Class Declarations and Modularity
With support for Modules in TypeScript, which also aligns with an emerging proposal from ECMAScript 6, TypeScript supports targeting popular module loading specifications, including CommonJS and AMD in any ECMAScript 3-compatible environment. AMD allows users to not only load these modules of code at runtime, but to use the dependencies between them to load groups of related modules as needed automatically. The TypeScript compiler supports generating AMD from TypeScript modules, giving websites the potential to scale to large application sizes.
Open and Interoperable
TypeScript is open. The TypeScript language is made available under the Open Web Foundation’s Final Specification Agreement (OWFa 1.0), and we invite the community to discuss the language specification. Microsoft’s implementation of the compiler is also available on CodePlex (with git) under the Apache 2.0 license. There you can view our roadmap, and over the next few weeks and months you’ll see the TypeScript team continue to develop on CodePlex in the open.
Give Us Feedback
Just a few weeks ago, we launched Visual Studio 2012, and we’re actively working on “VS Updates” to deliver continuous value for Visual Studio developers. At the same time, we’re planning for future major releases of our tools. Along with projects like “Roslyn”, TypeScript is one foray into making programming languages and tooling even more productive, and like "Roslyn", TypeScript is also an early preview. Pick it up, take it for a spin, and give us feedback. You can contribute by discussing the language spec or filing a bug.
I personally am super excited about what the impact of TypeScript can be on the world of software development, particularly in a world where there is so much momentum for the web programming model. This is another important step in the journey for great tools for standards web development from Microsoft.