Yugma is a free web conferencing service that enables people to instantly connect over the Internet and to collaborate using any application or software, using both Windows and Mac. Online collaboration is great solution for businesses that need to share information with their employees and clients, regardless where they are located..

Source: http://www.yugma.com/

Another dramatically different approach that I know --- the RHUB web conferencing appliance which is an on-premise plug-and-play solution.