An introductory-level textbook in statistics covering descriptive and inferential statistics. Each chapter has links to related texts, instructional demos, and free statistical analysis programs. Author is David M. Lane, Rice University dep...
Sage is a free open source mathematics software system spanning a huge range of mathematics including algebra, calculus, combinatorics, number theory and graph theory.
RANDOM.ORG offers true random numbers to anyone on the Internet. The randomness comes from atmospheric noise, which for many purposes is better than the pseudo-random number algorithms typically used in computer programs.