TechCrunch has leaked video footage of an unreleased Google Voice Desktop App for Mac.
Unfortunately they believe the application has been put on hold since Google founders Larry Page and Sergey Brin don't want the company to make applications that aren't web based.
We've asked our sources for screen shots of what Google Voice Desktop looks like. We didn't get those, but we did get something better - the actual application. We've taken a video (above) showing what the application looks like, showing both outbound and inbound calls. This is mostly still branded Gizmo5, although the sign up screen says "Gizmo5 by Google," and it is fully integrated with the Google Voice service, address book, etc. The Desktop application was also automatically added as one of my phones in the Google Voice for the browser. We don't know if this is the current internal release or something more dated.