Microsoft Lync, a simple yet powerful feature rich communication system, which includes the following features:
- Your Present Status of Availabilities
- Instant Messaging
- File Sharing
- Voice Communication
- Multi-Party Conferencing
- PSTN to Lync & Vice Versa Communication through Media Gateway
But Lync is only used for Enterprise Grade Communication Solution, the predecessor was OCS; the Office Communication Server. Now the funny thing is that it has a robust feature like RTA and RTV; real time audio and video codecs. And your contacts could be stored in groups, can chat with them of which the conversation will be stored in the “Conversation History” folder of Exchange Server/Outlook. Delete your friends from the group or block them, the blocked users will not be notified of the block, so noone gets hurt 🙂
Now, similar experience can be achieved through O365 as well.
More information follows: http://technet.microsoft.com/en-us/library/lync-online-instant-messaging-presence-and-contacts.aspx