GVoice is a new Google Voice client for Windows Phone 7. What makes it different from the other 3 Google Voice clients in the marketplace (GV for Windows phone, GoVoice and GV Companion) is that it is being developed by Koushik Dutta, the hacker who was responsible for creating a standard accelerometer software interface widely used on Windows Mobile handsets, and of course also Klaxon, a very full featured alarm app.
Of course he was seduced by the siren call of Android, so it is very welcome to see him back on a Windows phone platform.
Possibly more significant however is that the software uses push notifications and a live tile to notify users of text messages and new voice mails, using the apps own servers. Read more about that here.
The app is not in marketplace, but will hopefully show up soon. In the mean time you can follow his progress at ClockworkMod here.