Android: We all have that friend who likes to thumb through your photos when you show them a picture on your phone. Focus lets you prevent this intrusive behaviour by only allowing the user to view one picture, secured by a PIN.
When you want to show a picture to a friend, tap the share button and send the picture to Focus. The app will then only allow the user to view that single picture. If they try to swipe left or right, they won't see anything. Pressing Back will prompt the user to enter a 4-digit code. If the user presses the Home button, your phone will ring and/or vibrate depending on your settings.
It's not a full-blown security app (if you want to protect your...sensitive pictures, you can check out our guide here), but for preventing your friends from getting nosy, it gets the job done.