A few days ago Microsoft announced a new programming language, TypeScript. Effectively, it is a typed super-set of JavaScript that compiles to “normal” JavaScript. Being super-set also implies that JavaScript programs are also TypeScript programs, so one can reuse all the existing code-base and external libraries, while still benefiting higher productivity, new language features, and new tools (e.g. there is a VS2012 plugin with full IntelliSense).
The thing looks quite interesting, solid, and extra credibility is added by the fact that Anders Hejlsberg himself made almost an hour long Introducing TypeScript video about the subject. Of course, it is not guarantying that the project will survive in the long-term, but then, on the other hand, the risk of using TypeScript in own projects is minimal, even non-existing, as you always end up with normal JavaScript, so you can migrate back to JavaScript-only development any time you wish.
Scott Hanselman also expresses his view about TypeScript in Why does TypeScript have to be the answer to anything?. The article has some explanations, and references some extra tools, e.g. Web Essentials 2012 VS2012 plugin that, among many other cool things, improves TypeScript support in the VS2012.
Roman Hnatiuk 