Snapchat - Real-time picture chatting
Mirage - Mirage is a fast and simple GTK+ image viewer.
Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.
Postman - The Collaboration Platform for API Development
StealthChat - StealthChat is Encrypted, Private, Secure Calls and Chats on Android and Apple iOS
Ristretto - The Ristretto Image Viewer is an application that can be used to view, and scroll through images.