TypeScript is a new language from Microsoft that adds type safety to JavaScript.
I wrote a presentation on Microsoft TypeScript using a nice slideshow framework called reveal.js. After using it for several months, I can say that Microsoft has done a great job at creating a language that ehances JavaScript without trying completely overhaul the language. In fact, they are trying to align TypeScript with ES6 so that we can begin using the new features before browsers even implement them!
I highly recommend TypeScript to anyone working on large-scale web apps with more than a couple javascript files. The beta is solid and 1.0 is going to be even better!