Facebook lacks the functionality to notify Facebook users while their friends come online to Facebook Chat. So here is a free application available, entitled Facebook Friend Alert that creates popup alerts when your friends get login to Facebook so you can start Chat.
Facebook Friend Alert only notifies for Facebook Chat not for Facebook that means if your friends have enabled Facebook Chat then you will get notifications when they are availabile on Facebook Chat.
Facebook Friend Alert is a Windows application and works with all major web browsers like Microsoft Internet Explorer, Mozilla Firefox and Google Chrome. So, just download and install Facebook Friend Alert it and look how it works and also write your experience in comments.
Download Facebook Friend Alert