If you are looking for the software, go to the official reWASD website. But if you are looking for the , GitHub is the right place to look.
ReWASD is a software that allows you to remap your keyboard and mouse inputs to your gaming controller, and vice versa. This means that you can use your controller to play games that don't natively support it, or customize the layout to suit your playstyle. With ReWASD, you can create complex button mappings, adjust deadzones, and even create custom profiles for different games.
First, the elephant in the room: It is developed by a company (Disc Soft) and is a paid, proprietary software. You won't find the official source code on GitHub because the developers keep it closed to protect their licensing and business model.