<?php
$json='[
{"server":"1","available":true},
{"server":"2","available":false},
{"server":"3","available":true},
{"server":"4","available":true}
]';
var_dump(json_decode($json));

array(4) {
  [0]=>
  object(stdClass)#1 (2) {
    ["server"]=>
    string(1) "1"
    ["available"]=>
    bool(true)
  }
  [1]=>
  object(stdClass)#2 (2) {
    ["server"]=>
    string(1) "2"
    ["available"]=>
    bool(false)
  }
  [2]=>
  object(stdClass)#3 (2) {
    ["server"]=>
    string(1) "3"
    ["available"]=>
    bool(true)
  }
  [3]=>
  object(stdClass)#4 (2) {
    ["server"]=>
    string(1) "4"
    ["available"]=>
    bool(true)
  }
}