1)   Zim 2.0
Slim and simple chat and instant messaging server for Windows 2003/XP/2000 with support public and private chat channels, offline messages and file transfers through the server.

 2)   Express Messaging Server 2.0
Express Messaging Server 2.0 gives corporate message mates unparalleled speed for nonverbal communications using very low bandwidth. It provides a simple and intuitive user interface that lets you create accounts quickly and administer remotely.