Welcome to the PermissionsEx wiki!
PermissionsEx (PEX) is the oldest and most powerful permissions plugin available for Bukkit today. It has been around since the days of Permissions 2.x (in 2011) and continues to be supported and updated today.
But PEX is more! It offers different back-ends, powerful structured in-game command-management and fine grained restrictions set for world modification called Modifyworld