Syscall index: 0x1E13
Function signature: void APP_SYSTEM(void);
Opens the built-in "System" app.
On the "fx-CG10/20 Manager" emulator, the behavior is no different from the usual one, meaning that "unavailable" options remain locked.
Note that even though most built-in apps do not return, the calling code is kept on stack and one can return to it using a ugly hack, for example through timers, setjmp and longjmp. The reason why they don't return is that they expect to use GetKey as an exit point.