PhET now goes well beyond physics! Founded in 2002 by Nobel Laureate Carl Wieman, the PhET Interactive Simulations project at the University of Colorado Boulder creates free interactive math and science simulations.
HoodaMath.com is a free math games site. Founded by a middle school math teacher, Hooda Math offers over 350 Math Games.
Code.org® is a nonprofit dedicated to expanding access to computer science in schools and increasing participation by women and underrepresented youth.
PhysicsClassroom.com has been around since 1996! Very few web sites can say that and almost no education sites can. At physicsclassroom.com you can
And tons more!
A very useful site for learners and educators alike!