IntraMessenger : free corporate Instant messaging solution : opensource server PHP/MySQL (LAN Instant Messaging Software, LAN Messenger, Corporate IM, instant Messenger, IM Server, LAN Chat Server)

Users list
Can change name/function. Possibility to valid new user (see option _PENDING_NEW_AUTO_ADDED_USER).
Possibility to add users (see option _ALLOW_AUTO_ADD_NEW_USER_ON_SERVER).
Users roles management
If server option enabled, can add/remove rights for some users.
Updates options

See live server demo
Admin messages
The administrator can send (broadcast) messages (text or image) to users
Group managing
If option _SPECIAL_MODE_GROUP_COMMUNITY or _GROUP_FOR_SBX_AND_ADMIN_MSG activated.
Computers list
If option _ENTERPRISE_SERVER activated.
On this screenshot, menu is displayed on top.