Links

(AKA hoarded bookmarks)

Music/audio

The Conet Project Highly fascinating (and also creepy) recordings of shortwave numbers stations... Soundcloud/Internet Archive/Free Music Archive
Every Noise at Once A gigantic, messy map of musical genres.EDIT: Sadly, this site seems to be in a compromised state, due to the developer losing access to Spotify data (they explain it better on the site). Let's hope it lives on.
Radio Garden Possibly my favorite of all the sites, a sort of world map/radio tuner crossover. Move over the dots to listen to certain regions and stations within those regions.
University of Twente WebSDR From the University of Twente all the way in the Netherlands. This controls a shortwave reciever, allowing you to listen to shortwave radio and all that stuff from the comfort of your very own browser.

Fun/Games

Space Cadet Pinball A fully working in-browser port of the classic Space Cadet Pinball PC game
Minesweeper An in-browser port of the classic Minesweeper game (no bloat!!!)

"Tools" and useful stuff

Oblique Strategies A browser version of Brian Eno and Peter Schmidt's Oblique Strategies card "game," serving as prompts to get through creative block (although I have absolutely no idea how to use these). Wikipedia may explain better than I can.
7/6/24 EDIT: the old website that I used for this didn't seem to be working, so I replaced it with another one that seems to be basically the same.
Story Plot Generator From Big Huge Thesaurus, this is a random story plot generator if you ever need ideas/inspiration for writing. Some of these can get pretty absurd, and are good for a laugh (which is exactly why I like this).
List of Distracting Websites From Daniel Woodfield on Github. Pretty self-explanatory; use as you wish. Not comprehensive (as the internet is massive), but has a lot of 'em. Also be sure to check out ByteScout's List of Procrastination Websites.
sidenote: I would use this list with a website blocking browser extension; Leechblock is the one I use, and it's available for some of the most popular browsers. You know the ones...