It is a IDE toolkit. You're supposed to use it to build your own as can be seen in the "Arduino IDE Pro". They've used monaco[1] which is the editor part of VS

It is a IDE toolkit. You're supposed to use it to build your own as can be seen in the "Arduino IDE Pro". They've used monaco[1] which is the editor part of VS Code for their project but Theia apparently is easier to work on a cloud and customize. [1]: https://microsoft.github.io/monaco-editor/ https://microsoft.github.io/monaco-editor/