Developers may also use the Sisar or Easy SIS Creator applications, which provide a GUI for building SIS files. When the application is ready to be built, developers typically use the 'makesis' command, which is part of the CreateSIS utility. The PKG file must be defined by Symbian developers in order to build a single distributable SIS installer file.
You will most likely only encounter Symbian PKG files if you are developing an application for the Symbian OS.