Geometry

• Archimedes' Book of Lemmas - A collection of all 15 propositions from Archimedes' Book of Lemmas with complete proofs, each accompanied by a Java illustration.
• Bette Veteto's Homepage - History of Mathematics, very strong on geometry.
• Bob's Pages - A collection of interactive geometry applets. Topics include polyhedra, Poncelet's porism, Soddy's hexlet, Mandelbrot set, Steiner porism, Pappus's chain, Repulsion polyhedra and stereo pictures.
• The Complete Quadrilateral - Several properties of the complete quadrilateral illustrated with Java applets
• Conjectures Produced by the Program Graffiti - Graffiti is a computer program that makes conjectures in mathematics and chemistry. Links to the conjectures and bibliography.
• Cuboid and Cube Surface Distances - A java applet with substantial analysis related to distances on a rectangular box.
• Cut the Knot - Features articles about specific problems, illusions, and puzzles. Includes diagrams.
• Encyclopedia of Triangle Centers - By Clark Kimberling. Over 1000 triangle centres in a searchable compilation with diagrams.
• The Entropy Reduction Laboratory by Karl-Dietrich Neubert - Discusses double shell structured periodic systems, platonic spheres, molecular and crystal structures, and FlashSort algorithms.
• Erich's Packing Center - Graphics and links for various packing, tiling and covering problems.
• Fundamentals of Geometry - Free online book on geometry in pdf format. Contains material not easily found elsewhere from detailed exposition of elementary absolute geometry based on Hilbert's axioms to more advanced topics.
• A Gallery of Interactive On-Line Geometry - At the Geometry Center.
• Geometric Group Theory - Information and resources about geometric group theory and low-dimensional topology. People, groups, meetings, links.
• Geometry Activities - By Ephraim Fithian.
• Geometry and the Imagination in Minneapolis - Geometry exercises for a two-week summer workshop led by John Conway, Peter Doyle, Jane Gilman and Bill Thurston at the Geometry Center in Minneapolis, June 1991.
• Geometry Center - Web site for the (now closed) Center for the Computation and Visualization of Geometric Structures at the University of Minnesota. Graphics, multimedia, software, teaching resources.
• Geometry Formulas and Facts - Excerpts from the 30th Edition of the CRC Standard Mathematical Tables and Formulas (1995), namely, the geometry section minus differential geometry.
• Geometry from the Land of the Incas - Presents problems involving circles and triangles, with proofs, SAT practice quizzes and famous quotes. Also, has examples of geometry in Peruvian culture.
• Geometry in Action - Includes collections from various areas in which ideas from discrete and computational geometry meet real world applications.
• The Geometry Junkyard - Usenet clippings, web pointers, lecture notes, research excerpts, papers, abstracts, programs, problems, and other stuff related to discrete and computational geometry.
• Geometry Page from Interactive Mathematics Miscellany - Includes articles on topics in elementary and not so elementary geometry, many with interactive Java illustrations and multiple proofs.
• Geometry/Topology at Michigan State University - Activities of the geometry/topology group at Michigan State University.
• GLaD Comments - A new type of geometric construction that was discovered by Dan Litchfield and David Goldenheim. Includes general explanation and sketch examples.
• Go Geometry - Offers a variety of resources for teaching and learning about geometry. Problems and theorems are presented with step-by-step solutions for each proof.
• The Kepler Conjecture - Information on the recent proof of Kepler conjecture on sphere packings.
• The Lepidoptera of the Circles - The Butterfly theorem and its generalizations illustrated by Java applets.
• Math 3210 - Higher Geometry I - Course notes by Bill Cherowitzo.
• Math Forum: Geometry.research - Discussion board for geometry professors and instructors to keep informed of the latest research.
• Math Forum: Search geometry-forum - Those interested in examining the previous incarnation of the Math Forum may search the archives of the Geometry Forum.
• Mathematical Curves and Surfaces - Graphical representations of computer generated forms. (French/English).
• Morley's Miracle - A discussion of Morley's famous theorem and the research of which it was a tiny part. 5 proofs are given including J. Conway's, D. Newman's, and A. Connes'.
• New Mathematical Findings by Secondary Students - High school students solve complex geometric problems by using GLad Sketchpad. Page includes diagrams.
• Packomania - Includes packings of equal objects in containers together with source codes to obtain them numerically.
• Paul Bourke's Geometry Page - Includes formulas, definitions and three dimensional image illustrations.
• Polyedergarten - Shows paper models of polyhedra.
• Problem of the Minimum Rotation Surface - Java applet demonstrating the catenary.
• Sangaku: Reflections on the Phenomenon - Critical reflections on the sangaku phenomenon accompanied by a collection of solved sangaku problems, many with interactive Java illustrations.
• Steiner Surfaces - Mathematical descriptions and ray-traced images of various types of Steiner surfaces.
• Tim Lister's Hyperbolic Geometry - Cabri constructions for the demonstration of the basic concepts of hyperbolic geometry in the Poincare disc model.
• Wilson Stothers' Inversive Geometry and CabriJava Pages - Includes Steiner's Porism and the arbelos.
• Xah's Personal Page - Features an illustrated dictionary of special plane curves, a paper on wallpaper groups, mathematics image gallery and links to software packages.

• NPR : Mathematicians Get Crafty with Geometry - A husband and wife from Cornell University have come up with a crafty way to illustrate high-level geometry concepts -- by manipulating yarn into models that help explain the curvature of spaces. The mathematicians talk with NPR's Jacki Lyden about hyperbolic crocheting. [4:47 streaming audio broadcast] (March 13, 2005)

Other links and resources here.