Microsoft Lync Server 2010 SDK http://www.microsoft.com/downloads/en/details.aspx?FamilyID=58ccf6fd-31db-4f15-bafb-c5ef28afc5fc
Microsoft Unified Communications Managed API 3.0 Software Development Kit http://www.microsoft.com/downloads/en/details.aspx?FamilyID=4493BAAB-6214-4770-8CF9-69C813E8A9FA
Microsoft Unified Communications Client API SDK
http://www.microsoft.com/downloads/en/details.aspx?FamilyID=82c468da-3294-4ca9-bbcc-d455cfd06af2