nik_neman,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/themes/smoothness/jquery-ui.css">
<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/jquery-ui.min.js"></script>
<script>
$(function() {
var num = 0;
$('.add').click(function(e){
e.preventDefault();
var lastRepeatingGroup = $('.repeating').last();
var cloned = lastRepeatingGroup.clone(true);
var html = cloned.html().replace(/\d+/g, ++num);
cloned.html(html).insertAfter(lastRepeatingGroup);
});
});
</script>
</head>
<body>
<input name="" type="button" value="add" class="add">
<div class="repeating">
<input type="text" name="group[0][title]" id="title">
<input type="text" name="group[0][description]" id="description">
<input type="text" name="group[0][summary]" id="summary">
</div>
</body>
</html>