Please make sure to read this page: http://sourceforge.net/p/sipe/wiki/Frequently%20Asked%20Questions/
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)