Open Source DevTools by Microsoft
Disclaimer: Currently I am employed by Microsoft, but my views and thoughts are still my own. The reason I joined Microsoft was, the work Microsoft have been doing for last couple of years in Open Source Space. Today I am a advocate for Open Source representing Microsoft.
.NET Core
In 2014, Microsoft announced that, .NET will be both Open Source and Cross Platform. Back then it was one of the most surprising moves from Microsoft. Making one of its core platforms open source was unheard from Microsoft, and not just open source, but also cross platform. Until then Microsoft has reputation of being Windows only and being against open source.
Visual Studio Code
Today VSCode (Visual Studio Code) is one of the most used IDE's. As part of its cross-platform efforts, Microsoft released VSCode. VSCode is created entirely in JavaScript, it uses Electron for packaging and Monaco for the editor. In a 2019 Dev Survey by Stack Overflow, VSCode was ranked as the most popular IDE.
There are rumors in the community that VSCode is now a de facto IDE in Google.
TypeScript
TypeScript is an open source programming language. TypeScript is meant for the development of large applications, which are then transcompiled using JavaScript.
When TypeScript was released, it was called JavaScript for C# developers.