Crafty Syntax Live support Help - Free download and open source:
"A multi-user, multi-operator, multi-department live Help support chat system that allows the operators of the websites to monitor their visitors as they are browsing the site and proactively open a chat session with the visitor. Is in PHP and uses either Mysql or Text based database . Other features include AUTO INVITE!, referer tracking, page tracking, chat notification, user is typing message, multiple chat sessions, sound alert, leave a message if offline, push urls, quick responses, and multiple operators. runs on your server and is open source GPL."

http://www.craftysyntax.com/CSLH/