One of my small office clients uses MSN Messenger frequently to send quick messages around the office ("You have a call", "I have a question", etc.) and it works very well for their needs, but now that Microsoft is shutting down the service they asked me to find something they can use as a replacement. The easy answer would be to simply have them move to Skype since that is what Microsoft is pushing as the replacement. However, the insurance agency management system that the office uses does not play nice if Skype is installed. That's a fault of the agency manager and not Skype, but still it means that Skype is not an option. Searching online doesn't give many alternatives except AIM and Yahoo Chat, neither of which look very promising mostly due to pretty widespread claims of poor support and a large population of spammers (even more than MSN). A simple messenging client that I could set up locally with a 'server' running on their domain controller or one of the workstations would work just fine, but they don't have much of a budget for this (the boss wants free if possible) so the choices are pretty limited. Any suggestions?