Disclaimer: I don’t own or have any vested interest in this or any other apps nor am I responsible for how you or anyone else choose to use them. Do your own research and make wise decisions!
What It Does: Makes square photo collages in various formats.
What I Like: Diptic offers a large selection of collage formats. More impressively (to me), it allows me to adjust the borders not only back and forth but also one end of a line at a time. That feature comes in handy when my photos would look best not just stuck in an arbitrary format of squares or rectangles.
What I Dislike: I dislike two things about Diptic. First, there is no option to swap photos that have been imported into the app. If I decide the one on the left would be better on the right, I have to tap on each location to import the photo I want to that specific window of the collage. Second, the app seems to center each photo in its window and will not let me move it to center on something off-center. I usually work around this by adjusting the frames as I mentioned above.