phpFreeChat is a free, simple to install, fast, customizable and multi languages chat that uses a simple filesystem for message and nickname storage.

It uses AJAX to smoothly refresh (no flicker) and display the chat zone and the nickname zone. It supports multi-rooms (/join), private messages, moderation (/kick, /ban), customized themes based on CSS and plugins systems that allows you to write your own storage routines (ex: Mysql, IRC backends), and you own chat commands !