Just a Line lets you create drawings overlaid on things you see in real life.
Here's how the company describes the app:
"Just a Line is an AR Experiment that lets you make simple drawings in augmented reality, then share your creation with a short video. Draw on your own or with a friend, then hit record and share what you made with #justaline."
Just a Line is free to download and use, and you can learn more about it on the Google Play Store.