David MacKay has put the textbook he wrote online for everyone to download in a variety of formats. If you find it useful, consider buying a copy.
A command line utility that calculates the amount of informational entropy in arbitrary fields of data. Useful for cryptanalysis and data compression research
A website about randomness, (pseudo-)random number generators, and cryptographic entropy. Contains discussions of these topics as well as some online RNGs to play with.
Along with NIST SP800-22rev1 (statistical analysis of pseudo-random number generators), the Statistical Test Suite can be used to actually perform the tests outlined in this document. Runs under Windows, Linux, and Mac OSX. Written in C.
A free, open source mathematical processing system written in Python.
Exponential moving average. Used to smooth spikes out in a stream of numerical data.
Python module that implements the summarization of html and text using several different algorithms.