Red's source code can be found here: https://github.com/red/red. If you're curious, you can download an archive file locally (click the Clone or download button) and unzip it for a closer look, for example, inside your Red installation directory. Alternatively, with git installed on your machine, you can clone the source code with the following command:
git clone https://github.com/red/red.git
For easy reference, rename the source folder as red-source. Here is an overview:
You will notice that lots of source files have a .r extension, which means these are REBOL files. Indeed, at this stage, the Red framework is scaffolded ...