Chris Hlas, hlascs(at)uwec.edu
GraphCalc - 2D & 3D graphing calculator (win, linux)
How the West Was One + Three x Four - basic operations game (win, mac demos)
KSEG - interactive geometry (win, mac, linux)
Peanut Software - small math tools by Parris
Tux Math Scrabble - Scrabble-like game for writing math equations (win, linux)
Tux of Math Command - basic operations drill/game, similar to Missile Command (win, mac, linux)
GCalc - graphing calculator
GeoGebra - dynamic geometry
Logo - introductory programming/drawing
QuickMath - graphing and computer algebra system
*** Many of these require Java, a free download ***
Cut-the-Knot - interactive and challenging math puzzles
Fraction Frenzy - timed game of matching equivalent fractions (requires Shockwave)
MathForum - problems, math help, and more
NCTM Illuminations - interactive activities corresponding to the NCTM Standards
WebSudoku - Japanese logic puzzle