Snapchat

 Snapchat  is an ephemeral photo hosting silo where users post photos to their story, which are viewable for a limited number of seconds, sometimes a few times.

Features

 * Snapstreak: Displays the number of days that you and a friend have consecutively Snapped each other. If you and your friend don't both send a Snap within 24 hours, you will lose your Snapstreaks.

Outrageous terms & conditions
"You grant Snapchat a world-wide, perpetual, royalty-free, sublicensable, and transferable license to host, store, use, display, reproduce, modify, adapt, edit, publish, create derivative works from, publicly perform, broadcast, distribute, syndicate, promote, exhibit, and publicly display that content in any form and in any and all media or distribution methods"

Snapchat responded that "The Snaps and Chats you send your friends remain as private today as they were before the update." and "It’s true that our Terms of Service grant us a broad license to use the content you create—a license that’s common to services like ours. We need that license when it comes to, for example, Snaps submitted to Live Stories..."

Ephemerality Illusion
The 3rd party website SnapSaved.com claimed to save the Snapchat photos you received, which they did but for themselves also. SnapSaved did this by implementing the password-antipattern by asking for your Snapchat password.

https://pbs.twimg.com/media/BzmwphjCUAA2c9p.jpg

And then the site's creators released the photos:
 * 2014-10-10 Business Insider: Hackers Access At Least 100,000 Snapchat Photos And Prepare To Leak Them, Including Underage Nude Pictures