Google announced a brand new Gmail feature today: Video conversations in Gmail - called "Gmail Video and Voice".
This service combines the chatting abilities of GTalk, previously used in Gmail for chatting inside the browser. Google has now enabled full video, voice, and text chat inside the browser to Firefox, Chrome, or Internet Explorer users on Windows and Firefox users on the Mac, with possible expansion to Linux and mobile phones later. The service works by downloading and installing a small plugin which enables Gmail to use your webcam and microphone and enables the video and voice features of the service.
Gmail users will find this addition useful, because many of their existing contacts use Gmail or GTalk already, and no dedicated application is necessary.