chat for community site

Hello I have a community site, I want to add a chat service where registered people can privately chat each other. When a user want to chat with another user, he/she clicks a link and a private chat window opens, the receiver user will be notified in some way of the chat request and then clicking something will open the chat window to allow users to chat. I don't know what is the best technology to do this, you will suggest me this when posting your bid. Thank you ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform Linux server, Windows client, Internet Explorer, Firefox