chat

[Costas]

minimal PHP + jQ ajax - no database required (file based)
http://code.tutsplus.com/tutorials/how-to-create-a-simple-web-based-chat-application--net-5931
http://coursesweb.net/php-mysql/script-chat-simple_s2

Live helper chat
http://livehelperchat.com/

phpFreeChat
http://www.phpfreechat.net/

websocket
http://www.sanwebe.com/2013/05/chat-using-websocket-php-socket
http://github.com/PeeHaa/WebSocketDemo
http://code.google.com/p/php-websocket-server/
http://www.websocket.org/echo.html