Geometry

Bette Veteto's Homepage - History of Mathematics, very strong on geometry.
http://www.people.memphis.edu/~brveteto/

Geometric Group Theory - Information and resources about geometric group theory and low-dimensional topology. People, groups, meetings, links.
http://www.math.ucsb.edu/~jon.mccammond/geogrouptheory/

Polyedergarten - Shows paper models of polyhedra.
http://www.polyedergarten.de

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.
http://www.geom.uiuc.edu/docs/doyle/mpls/handouts/handouts.html

Packomania - Includes packings of equal objects in containers together with source codes to obtain them numerically.
http://hydra.nat.uni-magdeburg.de/packing/packing.html

Center of Points in 2- or Higher-dimensional Space - It provides important formulations for finding a center of points in 2 or higher dimensional space. It can be used in drawing delauney triagulation and voronoi diagram in two or higher dimensions. It also describes how many points are required in defining a center in n-dimensional space.
http://www.geocities.com/kiranisingh/center.html

A New Way to Calculate a Triangle's Area - Using the length of the three sides. The proof is better understood than the old one.
http://hometown.aol.com/tienchien/myhomepage/find_triangle_area.html

Tim Lister's Hyperbolic Geometry - Cabri constructions for the demonstration of the basic concepts of hyperbolic geometry in the Poincare disc model.
http://mcs.open.ac.uk/tcl2/nonE/nonE.html

Cut the Knot - Features articles about specific problems, illusions, and puzzles. Includes diagrams.
http://www.cut-the-knot.org/geometry.shtml

Geometry in Action - Includes collections from various areas in which ideas from discrete and computational geometry meet real world applications.
http://www.ics.uci.edu/~eppstein/geom.html

Geometry/Topology at Michigan State University - Activities of the geometry/topology group at Michigan State University.
http://www.math.msu.edu/gt/

A Gallery of Interactive On-Line Geometry - At the Geometry Center.
http://www.geom.uiuc.edu/apps/gallery.html

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.
http://www.geom.uiuc.edu/docs/reference/CRC-formulas/

Math Forum: Geometry POW/POM Search - Search the Geometry Problem of the Week's archive of creative, non-routine challenges, as well as submissions and commentary, dating back to 1993.
http://mathforum.org/powgrepform.html

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.
http://polly.phys.msu.ru/~belyaev/geometry.htm

Paul Bourke's Geometry Page - Includes formulas, definitions and three dimensional image illustrations.
http://astronomy.swin.edu.au/~pbourke/geometry/

Math Forum: Search geometry-forum - Those interested in examining the previous incarnation of the Math Forum may search the archives of the Geometry Forum.
http://mathforum.org/kb/forum.jspa?forumID=126

GLaD Comments - A new type of geometric construction that was discovered by Dan Litchfield and David Goldenheim. Includes general explanation and sketch examples.
http://jwilson.coe.uga.edu/Texts.Folder/GLaD/GLaD.Comments.html

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.
http://agutie.homestead.com/

Mathematical Curves and Surfaces - Graphical representations of computer generated forms. (French/English).
http://pagesperso-orange.fr/roger.assouly/

The Geometry Junkyard - Usenet clippings, web pointers, lecture notes, research excerpts, papers, abstracts, programs, problems, and other stuff related to discrete and computational geometry.
http://www.ics.uci.edu/~eppstein/junkyard/

Encyclopedia of Triangle Centers - By Clark Kimberling. Over 1000 triangle centres in a searchable compilation with diagrams.
http://faculty.evansville.edu/ck6/encyclopedia/

The Lepidoptera of the Circles - The Butterfly theorem and its generalizations illustrated by Java applets.
http://www.cut-the-knot.org/ctk/Lepidoptera.shtml

The Complete Quadrilateral - Several properties of the complete quadrilateral illustrated with Java applets
http://www.cut-the-knot.org/ctk/CompleteQuadrilateral.shtml

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.
http://www.gogeometry.com

Sangaku: Reflections on the Phenomenon - Critical reflections on the sangaku phenomenon accompanied by a collection of solved sangaku problems, many with interactive Java illustrations.
http://www.cut-the-knot.org/pythagoras/Sangaku.shtml

Math 3210 - Higher Geometry I - Course notes by Bill Cherowitzo.
http://www-math.cudenver.edu/~wcherowi/courses/m3210/m3210.html

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.
http://www.geom.uiuc.edu/

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 mathemeticians talk with NPR's Jacki Lyden about hyperbolic crocheting. [4:47 streaming audio broadcast] <small>(March 13, 2005)</small>
http://www.npr.org/templates/story/story.php?storyId=4531695

The Entropy Reduction Laboratory by Karl-Dietrich Neubert - Discusses double shell structured periodic systems, platonic spheres, molecular and crystal structures, and FlashSort algorithms.
http://www.neubert.net/

Geometry Activities - By Ephraim Fithian.
http://homepage.mac.com/efithian/geometry.html

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.
http://members.ozemail.com.au/~llan/

Problem of the Minimum Rotation Surface - Java applet demonstrating the catenary.
http://home.ural.ru/~iagsoft/PMRS_J.html

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.
http://www.cut-the-knot.com/geometry.html

Steiner Surfaces - Mathematical descriptions and ray-traced images of various types of Steiner surfaces.
http://www.ipfw.edu/math/Coffman/steinersurface.html

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.
http://xahlee.org/PageTwo_dir/more.html

Math Forum: Geometry.research - Discussion board for geometry professors and instructors to keep informed of the latest research.
http://mathforum.org/kb/forum.jspa?forumID=130

Cuboid and Cube Surface Distances - A java applet with substantial analysis related to distances on a rectangular box.
http://www.btinternet.com/~se16/js/cuboid.htm

The Kepler Conjecture - Information on the recent proof of Kepler conjecture on sphere packings.
http://www.math.pitt.edu/~thales/kepler98/

New Mathematical Findings by Secondary Students - High school students solve complex geometric problems by using GLad Sketchpad. Page includes diagrams.
http://www.javeriana.edu.co/universitas_scientiarum/vol6n2/ART1.htm

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'.
http://www.cut-the-knot.com/triangle/Morley/index.html

Wilson Stothers' Inversive Geometry and CabriJava Pages - Includes Steiner's Porism and the arbelos.
http://www.maths.gla.ac.uk/~wilson/cabripages/inversive/inversive0.html

Erich's Packing Center - Graphics and links for various packing, tiling and covering problems.
http://www.stetson.edu/~efriedma/packing.html

Archimedes' Book of Lemmas - A collection of all 15 propositions from Archimedes' Book of Lemmas with complete proofs, each accompanied by a Java illustration.
http://www.cut-the-knot.org/Curriculum/Geometry/BookOfLemmas/index.shtml

Conjectures Produced by the Program Graffiti - Graffiti is a computer program that makes conjectures in mathematics and chemistry. Links to the conjectures and bibliography.
http://cms.dt.uh.edu/faculty/delavinae/research/wowref.htm