This article described how to shut off Lync tabbed conversations within the Windows client.
When using the Lync 2013 client on your desktop, it automatically defaults to tabbed conversations meaning that ALL conversations you have going will stick in one window. For some, this may be ok, but if you are transitioning from Office Communicator to Lync in your environment, you have grown used to having multiple windows along the bottom of your screen.
Thankfully there is a way to shut this off within Lync 2013. While in the Lync client, click on the gear icon towards the top, go to TOOL > OPTIONS. In the general selection, you will notice ENABLE TABBED CONVERSATIONS is checked. Simply uncheck this box and that is it!!