IM2001Server is a freeware instant messaging software for Windows that works in your LAN on Internet.

This software is under developing from a community of developers so it's totally freeware (at least the beta version).
This software contains two parts: the server and client; both are for Windows and are fully functioning without any restrictions.
At date of today there are already hundreds of users and many companies are adopting this service instead of classical Microsoft Messenger, AOL IM, Yahoo messenger, ecc. since there are security problems; with this software you can set up an internal instant messaging service within your company and use new incoming comunication channel is growing daily!.
Here some feature built inside of this software:
Any message has been encrypted before being sent on the network and only the recipient can decrypt it. Also any comunication through client and server has been encrypted.
The messages has been encrypted two times and also a digital check has been applied in order to guarantee the message integrity.
Any message has a return receipt, so under stress conditions the messages will be sent and delivered even if the user is offline!
All comunications stay on local network so no information jump on Internet
AOL IM is integrated within IM2001
A complete list of functionalities on the official site http://www.geocities.com/instantmessaging2001