MyAppSharer let you to easy share your apps to your friends or backup, you can share by link of Google play or directly share APK (App's full package).
MyAppSharer support many method to share your apps, you can share by message, Gmail, bluetooth, what's app, facebook, QR-Code, Dropbox etc..
By using the feature to export APK to SD card, you could backup your app to your SD card.
MyAppSharer also support share multiple apps at one time, and support instant search, easy to find your apps.

Here is a demo video for sharing apk between devices.
Thanks "Flo WolfOne" provide the video.
https://www.youtube.com/watch?v=ETuLrn3QK2U

* Nexus devices could not receive APK via Bluetooth, to workaround this issue, please use "Android Beam" or "Bluetooth(zip)" instead.

p.s.
1. You can install "Barcode scanner" to support share link by QR-Code.
2. Install "Dropbox" to support share APK to Dropbox.
3. If you like the app, you could donate the app from settings menu to remove Ad.

Disclaimer: Before share APK, please make sure you have the redistribution right.