Creative Commons Zero (CC0 1.0 Universal)

From the developer's own README (https://github.com/ncase/wbwwb):

"I'm releasing all my code and art to the public domain, under the Creative
Commons Zero un-license (http://creativecommons.org/publicdomain/zero/1.0/).
Which means if you wanna remix this to make your own way-too-meta game, or
use it in a presentation or classroom or whatever, you already have my
permission!"

Third-party code bundled with the game (per the same README):
- PIXI.js, for rendering the graphics (MIT License)
- Howler.js, for playing the sounds (MIT License)

Several individual sound effects are separately credited as CC BY or CC0
from freesound.org contributors; see the README above for the per-sound
attribution list.