My favs are:
Brilliant.org - cool courses in computer science, math and logic. Great stuff to educate yourself.
Also I'm a big fan of Gen.lib.rus.ec - huge online library of books: science, math, biology, economics. You could find almost anything.
Boxopus.com - my ISP blocks torrent traffic so I'm using this online torrent downloader.
Notion.so - super useful workspace. I use it to put all my notes, links, video.
Producthunt.com - place to find new cool services and apps.