Threema is a messaging app for mobile which puts security first. It was developed by kasper systems with aims of providing users with true end to end encryption. That means, you can rest assured that only you and the recipient can read or see your messages. The developer lists the following features of Threema in play store:
-End-to-end encryption of text messages, images, videos and GPS locations
-Contact synchronization (optional): find other Threema users automatically
-Verify your contacts' public keys by scanning a QR code from their mobile phone, all within the app
-Send images and videos
-Share your location on a map.
You can download and install Threema Android apk from the official page
here or alternatively, get
more info here.