Visual Studio Code is already built on top of a number of open source projects we've created or are contributing to, including the Roslyn compiler and language

Visual Studio Code is already built on top of a number of open source projects we've created or are contributing to, including the Roslyn compiler and language tools, OmniSharp, Typescript, and GitHub Electron. We are still in an early stage and we're evolving our architecture - and we'll look at what we open source, and how we do it, as part of that.