Icons are sourced from various places:

* https://game-icons.net/
* https://commons.wikimedia.org/wiki/Main_Page

Fonts:

* https://github.com/adobe-fonts/source-sans
* https://github.com/adobe-fonts/source-serif
* https://www.google.com/get/noto/

Image processing software:

* https://github.com/google/guetzli/
* https://github.com/mozilla/mozjpeg
* https://github.com/svg/svgo
* http://optipng.sourceforge.net/
* http://potrace.sourceforge.net/