Visual Studio Code is a versatile cross-platform text editor. It has been developed by the VS Code team at Microsoft and the source code is distributed under the terms of the MIT License.
It’s worth noting that their official binaries are not fully open-source, however, as they come bundled with Microsoft branding, telemetry and licensing and are released under the Microsoft Software License Terms. To avoid this, you’re free to compile it yourself using the source code, or you can download VSCodium instead. I use VSCodium myself and can highly recommend it.
There are a large number of useful extensions for VS Code that you can find in the Visual Studio Marketplace or, alternatively, the Open VSX Registry. I’m listing the ones I use here. Most of these are highly configurable, so you can customise them to suit your needs.
To develop in Windows Subsystem for Linux (WSL), VS Code for Windows must be installed along with the WSL Remote Development extension. Read the docs for more information.