OfficeSIP Alerter is a simple, easy-to-use and free sip messenger. It was not designed for prolonged chat, it is handy when you need to send or receive single message. It is good replacement for old-fashioned Alerter Service.

OfficeSIP Alerter has simple interface but it is based on Session Initiation Protocol, therefore you will be able to exchange messages with any user of Windows Messenger or other sip messenger.