注意：当从数组值动态调用方法时，数组到字符串转换

index.php

include_once "system/libs/Main.php";
include_once "system/libs/FController.php";

$url = $_GET['url'];
$url = rtrim($url,'/');
$url =explode("/", $url);

include('app/controllers/'.$url[0].'.php');

$ctlr = new $url[0]();
$ctlr->$url[1]();

======================

If echo from array index it is Ok. and when I call method directly it also Ok.

but when I call method dynamically from array index value it says: "Notice: Array to string conversion".

Try surrounding the $url[1] with brackets (but be aware executing PHP by $_GET isn't the best for security).

Your code should then look like this:

$ctlr->{$url[1]}();