Saga Back to the Future easter egg
Saga, a lifelogging app for learning more about your daily habits, has some fun polish for when you’re traveling at just the right speed. As a lifelogging app, it’s designed to sit in the background, passively and privately log your steps and the places you go, then tell you interesting things about your (and, optionally, your friends’) daily habits.

In this case, I was on an Amtrak train, and the developers added an easter egg for just such an occasion.