A Gallery of Interactive On-Line Geometry

At the Geometry Center.

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

Bette Veteto's Homepage

History of Mathematics, very strong on geometry.

http://umdrive.memphis.edu/brveteto/www/

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/

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

Cut the Knot

Features articles about specific problems, illusions, and puzzles. Includes diagrams.

http://www.cut-the-knot.org/geometry.shtml

Encyclopedia of Triangle Centers

By Clark Kimberling. Over 1000 triangle centres in a searchable compilation with diagrams.

http://faculty.evansville.edu/ck6/encyclopedia/ETC.html

Erich's Packing Center

Graphics and links for various packing, tiling and covering problems.

http://www.stetson.edu/~efriedma/packing.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

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

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/

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/

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/

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

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/

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/

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/

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

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

Mathematical Curves and Surfaces

Graphical representations of computer generated forms. (French/English).

http://roger.assouly.pagesperso-orange.fr/

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]

http://www.npr.org/templates/story/story.php?storyId=4531695

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

Polyedergarten

Shows paper models of polyhedra.

http://www.polyedergarten.de/

Problem of the Minimum Rotation Surface

Java applet demonstrating the catenary.

http://home.imm.uran.ru/iagsoft/PMRS_J.html

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

The Complete Quadrilateral

Several properties of the complete quadrilateral illustrated with Java applets

http://www.cut-the-knot.org/ctk/CompleteQuadrilateral.shtml

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/

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/

The Lepidoptera of the Circles

The Butterfly theorem and its generalizations illustrated by Java applets.

http://www.cut-the-knot.org/ctk/Lepidoptera.shtml

Wilson Stothers' Inversive Geometry and CabriJava Pages

Includes Steiner's Porism and the arbelos.

http://www.maths.gla.ac.uk/wws/cabripages/inversive/inversive0.html