Lync Server 2013 beta was released by Microsoft today. Here are some useful and download links to get started:

Lync 2013 public beta home page

Lync Server 2013 public beta – Introduction & What’s new
Lync Server 2013 public beta – Download
Lync Server 2013 public beta – System Requirements
Lync Server 2013 public beta – Evaluation Resource Pages
Lync Server 2013 public beta – Technet Library Documentation
Lync Client public beta – (included in Office Pro Plus)

Have Fun