http://blogs.scientificamerican.com/roots-of-unity/2013/09/12/10-trig-functions-youve-never-heard-of/ Trig functions long forgotten to time.
http://www.gutenberg.org/wiki/Mathematics_%28Bookshelf%29 Project Gutenberg has started typesetting out-of-print math books in LaTeX.
http://thevirtuosi.blogspot.com/2011/10/linear-theory-of-battleship.html A look at a system that estimates the probability of ship placements in Battleship.
http://betterexplained.com/articles/a-visual-intuitive-guide-to-imaginary-numbers/ An explanation of how imaginary numbers work as a rotation.
http://www.cabinetmagazine.org/issues/16/crocheting.php An interview with two professors who crocheted hyperbolic shapes to demonstrate their properties.
http://blog.wolfram.com/2010/08/13/25-best-hangman-words/ This post comes up with a method to find the hardest to guess hangman words and gives a list.