Ask HN: Cool and Useful Dockerized Apps?

Recently seeing this testing mailserver linked on HN: https://tweedegolf.nl/en/blog/86/introducing-mailcrab

I was reminded of another useful tool, mimic3 by MycroftAI that gives you very nice TTS: https://github.com/MycroftAI/mimic3

So I was wondering: what other useful apps have been containerized for easy setup and great usefulness?

Basically the point of this question is to let people share these, for the benefit of all.