Doom Builder is an open source development released under GNU GPL. Everyone can learn from the source code and use it in a GPL compatible project. On this page you can find all resources related to the development of Doom Builder. You may also be interested if you want to make a plugin or your own game configuration.
The Doom Builder 2 source code is hosted on SourceForge and is available through SVN at the following location:
All Doom Builder 1 source files and resources used in the development. This program is released under GNU General Public License. This package does not contain system libraries used, you must install Doom Builder to ensure you have the required libraries.