Copyright is so fucked up that you can't create public domain resources because
all the very basic building blocks are copyrighted, even if freely licensed.

This is a list of some nice essential public domain building-block resources that
I have found.

FONTS
  dotcolon fonts:          professional fonts, all CC0, site is in Japanese, http://dotcolon.net/
    Aileron:               many variants, includes Czech accents, http://dotcolon.net/font/aileron/
    Medio:                 nice serif, one variant, no Czech glyps, http://dotcolon.net/font/medio/
    Vegur:                 https://dotcolon.net/font/vegur/
    Penna:                 https://dotcolon.net/font/penna/
    Seshat:                https://dotcolon.net/font/seshat/
    Ferrum:                https://dotcolon.net/font/ferrum/
    Eunomia (old):         https://dotcolon.net/font/eunomia/
    Tenderness (old):      https://dotcolon.net/font/tenderness/
  GirlsAreDumb:            fixed-size font, CC0, Czech glyphs, https://gitlab.com/drummyfish/fonts
  Mr Henry:                beautiful professionally looking CC0 sans-serif, has Czech glyphs, https://github.com/nickdaze/mr-henry
  unscii:                  monospace Unicode fonts, with Czech accents, all except one variant are in PD, http://pelulamu.net/unscii/
  CC0 on fontlibrary.org   there is a few CC0 fonts, https://fontlibrary.org/en/search?license=CC-0&order=
  Kenney:                  game oriented, simple, only a few glyphs, https://kenney.nl/assets/kenney-fonts
  monogram:                monospace pixel font (for games), https://datagoblin.itch.io/monogram
  PETSCII dont:            CC0 bitmap TTF font, https://github.com/josefnpat/cc0-custom-fonts/tree/master/PETSCII%20Commodore
  drummyfish's fonts       basic bitmap fonts, from moderate size to extremely small, https://opengameart.org/content/1bit-graphics-collection

SOUNDFONTS
  RKHive Unison:           small, reasonable quality, http://rkhive.com/banks.html
  RKHive Masterpiece:      small, reasonable quality, http://rkhive.com/banks.html
  DSoundFont:              big, https://sites.google.com/site/strixsoundfont/home
  VSCO CE:                 orchestral, https://vis.versilstudios.com/vsco-community.html

PALETTES                   (set of colors is not copyrightable, but rendering in an image can be)
  256 drummyfish:          general, HSL-based, computed, https://gitlab.com/drummyfish/palette
  256 drummyfish 2:        improved, https://gitlab.com/drummyfish/palette2

ICONS
  mapkeyicons:             quality but not very big CC0 icon font, http://mapkeyicons.com/