[10/21] M.C. Escher (1898-1972) was a Dutch artist well known for his often mathematically inspired woodcuts and lithographs. These feature tesselations, impossible constructions, explorations of infinity.
[10/19] Kali is a program that lets you draw patterns based on any of the 17 wallpaper groups, as well as several frieze and rosette groups.
[9/28] The Peaucellier-Lipkin linkage is a device that transforms straight-line motion into circular motion. It played an important role in the development of the steam engine.
[9/02] Geometry for Elementary School is a WikiBook with "ruler and compass" material and activities for elementary school students.
[9/02] GRACE (Graphical Ruler And Compass Editor) is an interactive ruler and compass construction editor for use in teaching the fundamental concepts of geometry to school students.
[9/01] Euclid's Elements are available online, courtesy of David Joyce at Clark University, Worcester, Mass.
[8/20] Textbook for Math 311: Symmetry, Shape, and Space (Key) by Kinsey and Moore.