A free app for Android, by Desygner Pty Ltd.

If you want to create beautiful collages, this app will help you. You can add multiple photos to a grid and change their sizes and positions. You can use free images from the Internet, or add your own.

Collage Maker will help you create a collage in minutes, even if you have no design experience. You will not need to worry about design or templates. It is easy to use and comes packed with all the tools you will need. It allows you to change fonts, colors, and add stickers. 

Collage Maker is a free app, but there are in-app purchases. However, you will not need to pay to download the app.