bookboon // for accounting, business, economics & finance, engineering, IT & programming, languages, marketing & law, natural sciences, statistics & mathematics (+ career & study advice, strategy & management)
booksee // for arts & photography, biographies & memoirs, business & investing, computers & internet, cooking, entertainment, health, history, home, law, literature & fiction, medicine, references, religion, science, sports, travel, and other categories
boundless // for accounting, algebra, art history, biology, business, calculus, chemistry, communications, computer science, economics, education, finance, management, marketing, microbiology, music, physics, physiology, political science, psychology, sociology, statistics, U.S. history, world history, writing
california learning resource network // for mathematics, science, history
ck-12 // for elementary math, arithmetic, measurement, algebra, geometry, probability, statistics, trigonometry, analysis, calculus, earth science, life science, physical science, biology, chemistry, physics, sat exam prep, engineering, technology, astronomy, english, history
college open textbook // for anthropology & archeology, art, biology & genetics, business, chemistry, computer science, economics, engineering & electronics, english & composition, health & nursing, history, languages & communication, law, literature, math, music, philosophy, physics, political science, psychology, science, sociology, statistics & probability
ebooklobby // for arts & photography, biographies & memoirs, business, computers & internet, cooking, entertainment, health, home & garden, law, literature & fiction, sports, travel
freemathbooks // for algebra, geometry, trigonometry, calculus, applied math, probability, analysis, statistics, and other sub-categories of mathematics
global text project // for business, computing, education, health, science, social sciences
openstax cnx // for arts, business, humanities, mathematics & statistics, science & technology, social sciences
open culture // for art history, biology, business & management, chemistry, classics, computer science & information systems, earth science, economics & finance, education, engineering, history, linguistics, law, mathematics, music, philosophy, physics, political science, psychology, sociology
open textbook library // for accounting and finance, business, management & marketing, computer science & information systems, economics, general education, humanities & language, law, mathematics & statistics, natural & physical sciences, social sciences
textbook revolution // for biology, business & management, chemistry, computer science & technology, earth sciences, economics, engineering, environment, ESL, health sciences & medical, mathematics, physics, society and social sciences, sociology, world history
bookstacks // popular classics
**If you know other helpful sites, please send me a message so I can add it to the list!
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