Islandoodle – free mouse-driven island creator
https://mattstark.itch.io/islandoodle

Random biome generator
https://perchance.org/fiction-biomes

BBC sound effects / soundscape generator
https://sound-effects.bbcrewind.co.uk/

Beepbox online music sketchbook
https://www.beepbox.co/

World Anvil, world-building toolkit, registration required
https://www.worldanvil.com/dashboard/

Very basic randomised setting generators
https://donjon.bin.sh

City creator
https://citycreator.com/