A plug-in adds a feature to ProBoard without changing ProBoard itself: a game, a chat client, a custom logon screen, a connection to a door network. v4 ships with several (see Plug-ins) and you can write your own.
A plug-in is an ordinary Windows DLL with the extension .P3X. ProBoard.exe loads it when a menu command asks for it, calls one entry point and gives it a table of functions to talk to the board: screen and keyboard, raw caller input and output, the current user, message areas, file transfers and so on. When the plug-in returns, the caller is back at the menu.
This replaces the old 16-bit PEX programs. Old .PEX files do not run on v4. The plug-ins that shipped with ProBoard have been rebuilt as .P3X and are installed for you.
.P3X file in the PEX folder./I, then the plug-in's name and any arguments, for example /I SAMPLEPLUGIN hello world or /I BBSLINK <game>.Some plug-ins are not on a menu. The login screens (AntiBot and PBMatrix) run during logon. See The Matrix logon.
PEX folder.See Writing a plug-in.