After encountering a public domain tileset on itch.io that appealed to me so much that I'm now considering experimenting with game development, I decided to start compiling a list of game assets on Itch.io that are under Debian-compatible licensing terms.
(i.e. Not the usual "don't redistribute or sell alone or in assets packs" terms which violate the FSF, OSI, and Debian definitions of Free and/or Open.)
https://itch.io/c/845926/libre-game-assets
(The description also lists other sources like OpenGameArt.)
@freemo Is it a roguelike? If so, 0x72's Dungeon Tileset (either version) is the best candidate I've found so far:
https://0x72.itch.io/16x16-dungeon-tileset
https://0x72.itch.io/dungeontileset-ii