Education (general):

- MIT OpenCourseWare
- - Free MIT course content.
- Khan Academy
- - Educational videos/tools.
- Wolfram Alpha
- - Computational knowledge engine that answers factual queries directly by computing the answer from externally sourced "curated data".

Mathematics:

- The Story of Mathematics
- - A history of mathematics & mathematicians.
- MathPages
- - Information on algebra/geometry/calculus/ et cetera.
- Octomatics
- - A base-8 number system.

Computer Science:

- The Jargon File
- - A comprehensive compendium of hacker slang.
- FreeTechBooks
- - Database of free/open access online computer science books, textbooks, and lecture notes.
- Grass (programming language)
- - A functional grass-planting programming language based on lambda calculus.

Philosophy:

- Basic Philosophy
- - A collection of fundamental ideas & a guide for the philosophically perplexed.
- The History of Philosophy
- - An interactive & visualized summary of the history of (Western) philosophy showing the connections between some of the key ideas/arguments of philosophers.