jamming.cat

Source on GitHub

jamming.cat: a cat that jams in your terminal

curl jamming.cat

A white cat bobbing its head to music
Colors
Size

Run it in a terminal and the cat jams along until you press Ctrl+C.

Full 24-bit color, which most modern terminals support. The cat takes up 48 columns and 24 rows.

Options
They're just parts of the address, so you can type them too: /party, /256, /ascii, /small, /big. Combine them like curl jamming.cat/party/big.
Windows PowerShell
Type curl.exe instead of curl.
wget or HTTPie
wget -qO- jamming.cat or http --stream jamming.cat