Slingshot is available for iOS and Android. The app is modeled on Snapchat and, like Snapchat, is designed to send self-destructing photo messages. Snapchat became popular for sending flirtatious selfies, and became more widely known because of scandals related to that use by public figures.
On Snapchat, people can see a photo sent to them by tapping on it and holding their finger down until it disappears, always within a few seconds. With Slingshot, recipients can see a message only if they send one back (hence the name). Until they do, they'll only see a pixelated preview of the image. After receiving the image, one swipes to dismiss it or taps it to send a response, after which the image is no longer viewable. Slingshot makes it easy to send photos to individuals or large groups of recipients. The app also has built in drawing features to share artwork or to draw on photos.
These new photo sharing apps were developed in response to privacy concerns and the right to be forgotten movement and to reduce the numbers of take down requests those things lead to. As seen with the hacking of Snapchat, however, the reality is that security and privacy are always a challenge, especially with a centralized target like a social sharing website.