The new IBM Lotus Sametime 8.5.1 release is GA today. Here are the system requirements.
Notabale additions are Mac and Linux desktop clients, Windows 7 client support, support for Notes and Domino 8.5.1 and 8.5.2 (when it is delivered) and a plan to add support for zLinux servers for IM and Meetings features within approx 60 days. We have also updated the mobile clients to support Blackberry 5.0 OS and Windows mobile 6.5.
Sametime 8.5.1 System Requirements