This is the newest experimental version of the GTalk client from the Google Labs. Looks pretty cool and neat. I installed it from their official site. However the download does not contain the software, rather its the installer only version which checks internet for the software and downloads it. Here is the official screen-shot and the download link.
This version features an integration with other GMail services like Orkut, Google Calendars and GMail. The integration with Calendars is cool, you get reminders at your desktop. I liked this feature a lot. But it has the possibility to irritate you in certain times for which you could turn it off like a "snooze" option.
The inclusion of Group Chat was a long desirable feature, this was only available in the web version of the client till now. The GTalk window has become multi-tabbed, which I do not think is a very good idea, but it does reduce some taskbar clutter in case of chatting with lots of friends.