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".
The Story of Mathematics
- A history of mathematics & mathematicians.
- Information on algebra/geometry/calculus/ et cetera.
- A base-8 number system.
The Jargon File
- A comprehensive compendium of hacker slang.
- 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.
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.