Info: This is a review of a paid application.
In-page/floating chat systems always existed but it was Facebook who made the experience slicker and really functional.
Using ArrowChat, a jQuery and PHP-powered chat application, it is possible to bring this functionality to any website easily.
Similar to Facebook chat, ArrowChat sits in the footer of the web pages, displays the other users online and allows each user to communicate with each other.

Besides 1-to-1 chats, chatrooms exist too and anyone can create new chatrooms (with passwords, moderators, kicking, etc.). There is also a pop-out option for chatting while browsing.
And, optionally, you can activate video chats as well. With a Flash-powered interface, users with webcams can video-chat instantly.
The system notifies users visually and with sound when a new request (chat, friend, private message..) is received. Also, it has an "announcement" feature where we can send a mass announcement to users and they will again be informed from the same notification interface.
ArrowChat bar can be extended with other apps like games, social links, translation shortcuts and much more. A store exists for getting such apps and more themes to change the design of the bar.

There is a powerful admin panel for controlling all the aspects of the application like managing users, themes and features.
In case you a re willing to use ArrowChat with a CMS, it is integrated with almost all of them (WordPress, Joomla, vBulletin, phpBB, etc.).
And, yes, mobile support exists too. The chat app works well on mobile devices.
The discount
ArrowChat is offering a 10% discount for all WRD readers who use the coupon code "WRDREADERS" and this is only available when checking out with credit/debit card.
P.S. The coupon code is valid until 31 October 2012.