In late April 2015, Microsoft announced that the popular Viber messaging services would be launching a universal Windows 10 app. Since then, there's been silence from both Microsoft and Viber on the status of the app, but a new message from Viber's PR rep indicates that it is still in the works.
Windows Central contacted Viber to get an update and received an email response from its PR representative merely stating that it is "still working on the universal app for Windows 10". However, the message didn't offer a release date estimate.
It would appear that the app is still a viable project, but that it may be a while before it appears in the Windows Store.
We are still waiting for many more promised major Windows 10 apps to be released, including ones for Instagram, Shopular and Facebook Messenger.