Free and Open Source Software is software that is developed by individuals and licensed in a fashion that makes the software available to all but enables further development by providing the source code that is used to compile or run the software. The license that is included is true of many real licenses in that it explains what you can and can't do with the software and your rights. One of the benefits of FOSS is that it satisfies long term support plans as the source code is included. I enjoy FOSS in my work as the community is typically made up of people that are truly interested in the goal of the software and are willing to work toward that goal.
Implementation is my primary role in FOSS while I do also preform integration and development from time to time. My work involves research, installation, configuration and trouble shooting. I typically make the most source code submissions to projects as I install and implement them and then help documentation efforts from there.
A great example of a project enabled by FOSS can be found at Linux Journal. This example shows how a corporate project enabled by FOSS can exceed expectations.