BZFS can be built to support the loading of external libraries as plug-ins. These plug-ins can alter or replace the logic applied by the server, as well as automate many common tasks. They are can be loaded at startup by the -loadplugin option, or at run time with the /loadplugin command.
Plug-ins are a simpler way to apply modifications to the game, as they do not require the server owner to modify or recompile his/her BZFS application. By using the BZFS API plug-ins are also able to be mixed and matched in an easy way.
Plug-ins are compile dynamic link libraries, that are built for the same OS/RuntimeEnvironment as the BZFS server that hosts them. On Microsoft Windows they are built as DLL files. On Linux and other Unix-like systems they are built as .so files.
On load, plug-ins install a number of callbacks and event handlers with the hosting BZFS that are called when specific events happen. This allows the plug-in to perform additional actions on these events, or if need be, alter the results of the default logic of the server.
Third Party Plug-ins
A number of non-developers have created plug-ins for BZFS, and usually release them on the BZFlag Forums.
Todo: describe the basics of plug-in development.