We offer a "live help" service to our customers. We used to use PHPLive! (paid app) until they vanished out of existence leaving us with several major security holes. We replaced that with Crafty Syntax Live Help (CSLH) which is open source and works reasonably well and seems to be pretty safe. I had it scanned by ScanAlert to test against XSS and SQL injection type attacks, and anything else that may raise alarms for "HackerSafe" certification.
The only feature we want that it doesn't have is "rate this operator" at the end of the chat session.