Single Variable Calculus, by M. Seppala
Calculus, by R. T. Smith and R. B. Minton
The Calculus Page Problems List, by D. A. Kouba
Visual Calculus
Cycloids
Cycloids, Hypocycloids and Epicycloids: [1] , [2] , [3]
Multivariable Calculus, by G. Cain and J. Herod
Level Curves Program, by B. Higgins