Viber was the least updated messaging app in the last year, but the wait is over.
Now we have a universal application for Windows 10 and Windows 10 Mobile.

Download Viber from Windows Store
[appbox windowsstore 9wzdncrfj46z]

The App adopted a new design language  that is very close to the Window 10 OS, and it seems that the app is more quicker than it was. I hope the old problems that the Windows Phone 8.1 version of the app, are gone and now it can be a reliable messaging and calling app.