The Duet is open source hardware, developed using open source tools, specifically KiCAD for the hardware design. You need at least version 4.0.2 to use the Duet 2 WiFi source files, along with the "complib" library. Newer projects now use KiCAD 5.0.
We encourage adaptation of the hardware design, get stuck in! Ensure you comply with the license terms.
RepRapFirmware, for controlling 3D printers and related devices, is also Open Source Software with source files available and actively maintained on Github. This repository provides a bug tracker, which is where you should file confirmed bug reports.
The Duet Web Control web interface source is Open Source Software with source files available and actively maintained on Github. This repository provides a bug tracker, which is where you should file confirmed bug reports.
Other repositories in the Duet ecosystem are available on Github here.
If you want to make a change to the code, the best approach is to fork the project, make some changes, test them on your own machine, and when they work file a pull request. Github will then support discussion of the pull request, which can ultimately be accepted into the main source code. Before submitting a pull request, please ensure that your changes conform to any coding standard that is used for that part of the software. The coding standard may be described in the readme file or in a separate file in the root of the corresponding GitHub repository.
The code is divided into several modules, and some modules use components from multiple repositories. If you plan to contribute your changes back to the main project (please consider it!), it is probably best to use https://git-scm.com/.
To compile a RepRapFirmware binary see the build instructions.