Cut-the-knot is a free, advertisement-funded educational website formerly maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003, the Encyclopædia Britannica's Internet Guide Award, and Science's NetWatch award. Its name is a reference to the legend of Alexander the Great's solution to the Gordian knot.
Cut-the-knot's manifesto states that "Judging Mathematics by its pragmatic value is like judging symphony by the weight of its score," and describes the site as "a resource that would help learn, if not math itself, then, at least, ways to appreciate its beauty." The site is designed for teachers, children and parents, and anyone else curious about mathematics, with an eye to educating, encouraging interest, and provoking curiosity. Many mathematical ideas are illustrated by applets.
CTK wiki (powered by PmWiki) extends the main site with additional mathematical content, especially that with more complicated formulae than available on the main site.
On Monday, July 9 2018, it was reported that Alexander Bogomolny had died. 
- "Cut-the-Knot's list of awards". Retrieved 2006-01-18.
- "Scientific American 2003 Sci/Tech Web Awards: Mathematics". Retrieved 2006-01-18.
- "Site Visit: Mathematical Wonders". Science. 285 (5424). 1999-07-02.
- "Cut-the-Knot's manifesto". Retrieved 2006-01-18.
- "Alexander Bogomolny, creator of Cut the Knot, has died". Retrieved 2018-07-09.