A free program for Android, by Pasha App.

Collage Maker: Photo Grid Photo Collage Maker is a free, easy-to-use application that lets you create various photo collages in a matter of seconds. This app allows you to import several images from your device and combine them in different ways. From simple grid layouts to freeform designs, there is a plethora of options for how you can combine your photos. The app also provides a bunch of editing tools such as crop, flip, rotate and more. And if you want to make your photos stand out even more, you can add text and stickers.

Collage Maker also allows you to create story templates so you can easily make a story for Instagram or Snapchat.