DPGraph + Viewer

Although the website is terrible, DPGraph is actually a very neat graphing application.

World Stats Clock

Everything Mathematical

MathematiciansPictures.com is a website about everything mathematical (pictures, t-shirts, etc.). If you're into math, you wouldn't be here otherwise, then visit that site for some neat stuff. Just come back afterwards. :-)

E-Tutor Graphing Calculator

E-Tutor has a nice, online, graphing calculator for visualizing equations.

Graph Layout Engine (GLEE)

GLEE is a .NET tool for graph layout and viewing. It has been developed in Microsoft Research by Lev Nachmanson. GLEE is built on principles of the Sugiyama scheme; it produces so called layered, or hierarchical, layouts. This kind of a layout naturally applies to graphs with some flow of information. The graph could represent a control flow graph of a program, a state machine, a C++ class hierarchy, etc.

Texmaker

Texmaker is a free LaTeX editor, that integrates many tools needed to develop documents with LaTeX, in just one application.

WZGrapher Function Grapher

WZGrapher is an easy-to-use and small-footprinted Function Graphing and Calculation Program written in C language, with capabilities to plot both cartesian and polar functions. WZGrapher can also be used to graph numerical solution curves of integrals, to solve numerically and graph ordinary differential equations up to the fifth order, and to calculate value tables (also of ODEs) including the first derivative values.

Orrery

An orrery or planetarium is a mechanical contrivance that reproduces the motions of the planets and, sometimes, of their satellites. Operated by hand using cranks or clockwork mechanisms. More information can be found here and here.

Vedic Mathematics

Vedic Mathematics is the name given to the ancient system of Mathematics which was rediscovered from the Vedas between 1911 and 1918 by Sri Bharati Krsna Tirthaji (1884-1960). According to his research all of mathematics is based on sixteen Sutras, or word-formulae. For example, "Vertically and Crosswise" is one of these Sutras. These formulae describe the way the mind naturally works and are therefore a great help in directing the student to the appropriate method of solution.

Here are some tutorials on it and some more information.

Group Explorer

Group Explorer is mathematical visualization software for the abstract algebra classroom. It helps the user visualize group theory, builds students' intuition, and enables experimentation with groups.

Mathematical Illustrations

Mathematical Illustrations is a book on mathematical PostScript programming and geometry. The website contains plenty of examples for downloading.

Binary Marble Adding Machine

This is a very cool description of an adding machine. Check out the original as well.

SITMO

SITMO is a LaTex equation editor. Check out the rest of their website for some other mathematical topics.

Public Implementation of a Graph Algorithm Library and Editor

P.I.G.A.L.E. is a graph editor and a C++ algorithm library essentially concerned with planar graphs. The editor is particularly intended for graph theoretical research.

Puzzlers Paradise

Puzzlers Paradise is a website with some great, interactive, logic puzzles.

PlotKit - JavaScript Chart Plotting

PlotKit is a Chart and Graph Plotting Library for JavaScript. It has support for HTML Canvas and also SVG via Adobe SVG Viewer and native browser support. Requires MochiKit - A lightweight JavaScript library.

WIRIS CAS Web Calculator

WIRIS CAS is an on-line platform for mathematical calculations designed for education. It is in fact a CAS that also includes a DGS inside. You can access a powerful calculation toolbar through an HTML page that includes integrals and limits calculation, function graphing in 2D or 3D or symbolic matrices manipulation. It covers all mathematical topics from High School to University level (Calculus, Algebra, …).