Mathematics #
★ POTI (Portuguese-only) - Free Math Olympiad summer classes with notes and sets of problems.
★ A Beautiful Journey Through Olympiad Geometry - Awesome Geometry book from Stefan Lozanovski.
★ Modern Olympiad Number Theory - Comprehensive textbook on Number Theory from Aditya Khurmi.
★ Instructional Systems’ resources for USAMO - A curated list made for USAMO contestants.
★ Evan Chen’s website - The Olympiad section and his syllabus are particularly interesting.
The Elements of Euclides (rather than paper) - A project that recreated Euclid’s Elements with interactive diagrams.
Contest Collections (AOPS) - Huge set of problems from past contests.
Yufei Zhao Handouts - Handouts from a Math Olympiad coach.
Rushil-verse (Rushil Mathur website) - Math Olympiads resources.
CS/Programming #
★ Developer Roadmap - A roadmap for aspiring programmers.
★ Project Euler - List of Math problems supposed to be solved using programming.
★ LeetCode - Similar to Project Euler.
Language Learning #
General #
★ Antimoon - Guide to learn English using the immersion-method.
★ Anki - Flashcard program using SRS (Spaced Repetition System).
Japanese #
★ jpdb - It’s a all-in-one learning system & dictionary, really.
★ The Moe Way - Awesome guide to learn Japanese.
★ Donkuri’s Guide - Immersion-Based Japanese Learning’s guide.
★ Jomako’s Guide - Has very nice Anki decks.
★ DJT’s Anacreon Resources - Has some Anki decks, media recommendations (by difficulty) and even polemic stuff!
★ Cade’s Guide
★ Japanese Core 6k Vocab - Seriously underrated vocab deck.
★ Jisho - English-Japanese dictionary.
★ Animelon - Free Japanese media (mainly anime).
★ Jimaku - Japanese subtitles for Anime and Live Action.
Kodansha Kanji Learner’s Course Anki deck with Vocabulary - Pretty self-explanatory.
Miscellaneous #
★ FMHY’s Educational Section - “Free-educational-media-heck-yeah”.
★ Project Gutenberg - Free and legal Ebooks of classic books.
★ 3Blue1Brown - Amazing educational content.
★ Wolfram Alpha - CoMpUtAtIoNaL PoWeR!!! Has many ways of using it.
Books’ Drive - A Google Drive full of books from a anon.