Much of the raw material for the first edition of this book came from five years of working with the Subversion project (http://subversion.apache.org/). Subversion is an open source version control system, written from scratch, which was intended to (and did for a while) replace CVS as the de facto version control system of choice in the open source community. The project was started by my employer, CollabNet (http://www.collab.net/), in early 2000, and thank goodness CollabNet understood right from the start how to run it as a truly collaborative, distributed effort. We got a lot of developer buy-in early on; today the majority of developers on the project are not CollabNet employees.
Subversion is in many ways a classic example of an open source project, and I ended up drawing on it more heavily than I originally expected. This was partly a matter of convenience: whenever I needed an example of a particular phenomenon, I could usually call one up from Subversion right off the top of my head. But it was also a matter of verification. Although I am involved in many other free software projects to varying degrees, and talk to colleagues involved in many more, one quickly realizes when writing for print that all assertions need to be fact-checked. I didn't want to make statements about events in other projects based only on what I could read in their public discussion archives. If someone were to try that with Subversion, I knew, she'd be right about half the time and wrong the other half. So when drawing inspiration or examples from a project with which I didn't have direct experience, I tried to first talk to an informant there, someone I could trust to explain what was really going on.
While Subversion was my full time job from 2000-2006, I've been involved in free software for more than twenty-five years. Other projects and organizations that have influenced this book include:
The GNU Emacs text editor project at the Free Software Foundation.
Concurrent Versions System (CVS), which I worked on intensely in 1994–1995 with Jim Blandy and was involved with intermittently for a few years afterwards.
The collection of open source projects known as the Apache Software Foundation, especially the Apache Portable Runtime (APR) and Apache HTTP Server.
The Launchpad.net project at Canonical, Ltd.
Code for America and O'Reilly Media, which gave me an inside view on open source civic technology development starting in 2010, and kindly kept me in the loop after I became a full-time consultant at Open Tech Strategies, LLC around 2012.
The many open source anti-surveillance and censorship-circumvention tools supported by the Open Internet Tools Project (OpenITP.org) and by the Open Technology Institute at the New America Foundation.
Checkbook NYC, the municipal financial transparency software released by the New York City Office of the Comptroller.
The Arches Project, an open source geospatial web application for inventorying and helping protect cultural heritage sites (e.g., historic buildings, archeological sites, etc), created by the Getty Conservation Institute and World Monuments Fund.
OpenOffice.org / LibreOffice.org, the Berkeley Database from Sleepycat, and MySQL Database; I have not been involved with these projects personally, but have observed them and, in some cases, talked to people there.
Likewise various projects at the Mozilla Corporation, including but not limited to the Firefox web browser.
GNU Debugger (GDB) (likewise).
The Debian Project (likewise).
The Hypothes.is Project (likewise).
This is far from a complete list. Many of the client projects I work with through our consulting practice at Open Tech Strategies, LLC have also influenced this book, and like most open source programmers, I keep loose tabs on a variety of different projects of interest to me, just to have a sense of the general state of things. I haven't named all of them here, but they are mentioned in the text where appropriate.
 Subversion was eventually supplanted by Git, one of several systems that implement "distributed version control", a style of working that is better suited to collaborative development than Subversion's centralized model.