AliveChat 

AliveChat allows you to connect with and track your web site visitors in real-time via a browser based live chat interface. Your company can now offer live support software to customers while increasing sales with Proactive chat.
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Boldchat Operator Client .NET 

Chat with visitors on your web site. Great for sales and customer service chats. See all visitors on your web site. Initiate chats with visitors. Customize your chat window with your logo, colors, etc. Display a chat button showing your availability.
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