Worldbuilding Pasta: Very in-depth guides to making the geography and climates of worlds. Also has climate explorations, such as what Venus's climate would be like if it was habitable.
Type IPA: Allows you to type IPA symbols and add diacritics to them.
Phoible: Shows the amount of languages each phoneme is used in.
Misc
Neal.fun: A bunch of neat things, such as the wildlife and depths of the deep sea, and an elevator to space.
If the Moon were only 1 pixel: Shows just how big the solar system would be if it were scaled down such that the Moon was the size of a pixel.
Wplace: Massive shared pixel art canvas on top of the world map. (Its moderation isn't super good, so you might see NSFW or bigoted things or get suspended for no reason)
Pokéfarm Q: Fan-made Pokémon browser game where you give EXP to people's Pokémon by clicking them, and most of them will click back.