Directory: Live support

This is a program very similar to other expensive Live Support Chats, xHTML and CSS compliant and...
Free and GPL.
It has also a WinApp but that is neither free nor GPL (but not too expensive).

PHP Live! (© OSI Codes Inc.) enables live customer support and visitor communication directly from your website. Provides real-time sales and/or customer service support from any computer, anywhere!

Open Source (not GPL) software that allows companies to have a powerfull CRM tool. More details in their website.

Customers want immediate responses to their questions. InstantService™ Chat delivers fast and consistent messaging while the customer is on your site. Our technology allows your company to serve a greater number of customers with existing resources. Your agents, empowered with InstantService Chat, can deliver real-time customer service that lowers abandonment rates, raises satisfaction levels and increases online sales.

RealTime Aide by TCCSoftware provides immediate, state-of-the-art messaging allowing your sales people to "chat" directly with customers while they are visiting your company's Web site.

A multi-user, multi-operator, multi-department Live Help support chat system that allows the operators of the websites to monitor their visitors as they are browsing the site and proactively open a chat session with that visitor. The modular structure and open source code allows for the highest level of freedom in customization to fit your needs.