Ask HN: Easter Eggs in Your Software

I remember being in school and being the only person who knew about the Microsoft Word Pinball easter egg. It required some special key presses, clicking the word logo in the right spot and then bam you could play a game in class :)

Easter eggs seem a lot more rare these days but I'm sure we all are still putting some in.

What easter eggs have you put into your software that you are most proud of?