To get an animation of the sea in ASCII on your terminal, install asciiquarium:
brew install cmatrixOnce installed, restart your terminal and run
asciiquarium
To stop the animation, use Ctrl-C.
So, what do I use this for? Nothing specific! Just enable it and relax! Bonus points if you fool your friends and get them thinking you actually have a fish tank full of fish! I've noticed that I get better results with my non-technical friends!
If you're interested in the source, check it out on GitHub.