<?php
error_reporting(-1);

$name = "заяц";

$letters = preg_split('//u', $name, -1, PREG_SPLIT_NO_EMPTY);


function ano($found, $letters) {
	if (empty($letters)){
		echo $found . "\n";
	} else {
		foreach ($letters as $num => $letter) {
			$tempArray = $letters;
			$tempAno = $found . $letter;
			unset($tempArray[$num]);
			ano($tempAno, $tempArray);
		}
	}

}
$here = "";

ano ($here, $letters);