Here is an extract and a link for further reading.
The Architecture of Open Source Applications
Chapter 25. Battle for Wesnoth
Programming tends to be considered a straightforward problem solving activity; a developer has a requirement and codes a solution. Beauty is often judged on the technical implementation's elegance or effectiveness; this book is replete with excellent examples. Yet beyond its immediate computing functions, code can have a profound effect on people's lives. It can inspire people to participate and create new content. Unfortunately, serious barriers exist that prevent individuals from participating in a project.
Most programming languages require significant technical expertise to utilize, which is out of reach for many. In addition, enhancing the accessibility of code is technically difficult and is not necessary for many programs. It rarely translates into neat coding scripts or clever programming solutions. Achieving accessibility requires considerable forethought in project and program design, which often runs counter-intuitive to normal programming standards. Moreover most projects rely upon an established staff of skilled professionals that are expected to operate at a reasonably high level. They do not require additional programming resources. Thus, code accessibility becomes an afterthought, if considered at all.
Our project, the Battle for Wesnoth, attempted to address this issue from its origins. The program is a turn-based fantasy strategy game, produced in an open source model based on a GPL2 license. It has been a moderate success, with over four million downloads at the time of this writing. While this is an impressive metric, we believe the real beauty of our project is the development model that allowed a band of volunteers from widely different skill levels to interact in a productive way.