From Lotus Notes/Domino

IBM Lotus Sametime is an enterprise instant messaging and web conferencing application. This software application provides enterprise instant messaging functionality, presence information, and web conferencing. It offers strong support for communications standards : it is integrated with Lotus Notes and Microsoft Office.

Lotus Sametime client software is available for Microsoft Windows, Linux, and Apple Macintosh. The Lotus Sametime server runs on Microsoft Windows, IBM AIX, i5/OS, Linux and Solaris.

Lotus Sametime is described in detail on the IBM product homepage. One of the features is Lotus Sametime Gateway, which adds support for communication with users of AOL, Yahoo and Google Talk. Lotus Sametime is built on the Eclipse platform, allowing developers familiar with the framework to easily write plug-ins for Lotus Sametime.