With QuickReplier for Viber, you can easily reply to Viber messages without having to open Viber app, whether you receive the message notification on lockscreen, in Notification Center or in some other app. Single and group conversations are supported, as well as sending pictures.
It is using Couria as the user interface, and supports Curia themes. (However, if Couria stops being actively developed I will roll out my own front-end interface.) Previous message history is displayed in the quick reply view when it pops up, and it is fully configurable.
Supported for Viber v4.2.1+. Future Viber app versions will be supported as well. Working on all iOS 6 and iOS 7 devices (iPhone/iPad/iPod Touch), including 64bit. iOS 8 support will be added when the time comes.
After installation & respring, please enable Viber plugin in Settings/Couria/Viber. Additional settings are available in Settings/ Couria/Viber/Other Preferences, where you can adjust the functionality to your liking.