7
Photo Collage App for Android
(discuss.tchncs.de)
F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The client makes it easy to browse, install, and keep track of updates on your device.
Matrix space | forum | IRC
If it's a simple combo of photos... Should be able to do it right in Google photos under the utilities tab.
Thanks for the hint. I haven't used Google Photos in a while and its features sound like what I want: https://support.google.com/photos/answer/12637115?hl=en&co=GENIE.Platform%3DAndroid
However, it is not an open source app.
Boo hoo. Get off your high horse. It works.