Wikipedia
#encyclopedia#reference#non-profit
The free encyclopedia — millions of articles in hundreds of languages, maintained by volunteers.
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Reading & Reference
Open-source software, free hosting, AI tools, and developer APIs.
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Wiktionary
#dictionary#reference#non-profit
Free multilingual dictionary project from the Wikimedia Foundation.
Wolfram Alpha
#maths#computation#reference
Computational knowledge engine. Free web tier answers most maths, science and data questions.
Project Gutenberg
#books#ebooks#public-domain
Free library of over 70,000 public-domain ebooks.
Standard Ebooks
#books#ebooks#public-domain
Free, beautifully formatted public-domain ebooks, hand-curated and proofread.
Internet Archive
#archive#books#non-profit
Non-profit digital library of millions of free books, films, music, software and web pages (via the Wayback Machine).
Open Library
#books#library#non-profit
Internet Archive project cataloguing every book ever published, with millions available to borrow free.
LibriVox
#audiobooks#public-domain#volunteer
Free public-domain audiobooks read by volunteers.
arXiv
#research#preprints#open-access
Free open-access archive of pre-prints in physics, maths, CS, biology and economics.
Google Scholar
#research#academic#search
Free search engine for academic papers and citations across publishers and repositories.
Semantic Scholar
#research#academic#ai
Free AI-powered academic search from the Allen Institute for AI.
DOAJ
#research#open-access#academic
Directory of Open Access Journals — free, peer-reviewed academic articles across disciplines.
PubMed
#research#medical#government
Free search of biomedical literature, maintained by the US National Library of Medicine.