php Free Chat is a simple, fast, and customizable chat server that uses the filesystem for message and nickname storage. It uses AJAX to smoothly refresh and display the chat zone and the nickname zone. It supports customized CSS stylesheets and a plugin system that allows you to write your own storage routines.
MOHA Chat is a chat solution which comes with a intuitive Web client and can run on most shared hosts. MOHA Chat consumes fewer resources on the server side and is fast on the client side. It uses AJAX to retrieve the chat messages and user status. The client polls the server at regular intervals. It currently supports only one-to-one chatting with the Web client. The Web client encrypts messages using a key unique to the client when sending a message to the server and vice versa.
Pandorabots Chat Bot Interface is a learning tool for implementing AJAX to communicate between the browser and a server. The chat bot interface communicates via XML with a free chat bot you create and host at pandorabots.com. The client script controlls a div that records your ongoing conversation. The final product is an embedded chat bot in your Web site.