Lync alternatives on Mac
I use Adium, there is an extension that lets you connect to Lync servers. 

Protocol plugin for Office 365/Lync/OCS


works only with:


  A third-party Pidgin/Adium/Miranda/Telepathy plugin for the extended
  version of SIP/SIMPLE used by various products:
  
  
  Skype for Business
  Microsoft Office 365
  Microsoft Business Productivity Online Suite (BPOS)
  Microsoft Lync Server
  Microsoft Office Communications Server (OCS 2007/2007 R2)
  Microsoft Live Communications Server (LCS 2003/2005)
  


Once you have the Xtra installed, you can add your Lync account as an "Office Communicator" account.