Citedbyjs is a project mainly written in RUBY and JAVASCRIPT, it's free.
A Cited-by widget that is easy to embed in any HTML page.
::
<meta name="dc.identifier" content="10.10/this_is_a_doi"/>
::
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
::
<script src="http://citedby.labs.crossref.org/citedby.min.js"></script>
Below is a complete example.
::
<html>
<head>
<meta name="dc.identifier" content="10.10/this_is_a_doi"/>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>
</head>
<body>
<div>
<script src="http://citedby.labs.crossref.org/citedby.min.js"></script>
</div>
</body>
</html>