Quik

easy to use mobile video editor by GoPro

Screenshots

Hunter's comment

Pros: easy, especially for changing video formats (horizontal, square, vertical) or making a video by still images.
Cons: can't have full length of the original video when it's edited.

You can check "How to use" on 1st and 2nd screenshots (better view on Steemit blog). It's just a few taps!
No problem with saving and sharing the video.

I edited my video like this. It seems "Dandy" is the best effect with its nostalgic atmosphere.