If you've got no idea what parametric functions are then read no further - this application will be a complete bore and mystery to you.
If however, you deal with parametric functions as part of mathematical or scientific research, then it could save you some major headaches. Curve Builder draws graph for parametric functions by allowing you to set real functions for each coordinate in 3D space.
Curve Builder draws graphs isometrically but it only gives you four viewing angles - front, left, from underneath and from above. However, that's all you'll probably need unless you're doing something particularly complex. Curve Builder also comes equipped with a zoom which, if your parametric graph is way too big for the screen, adjust it automatically to fit nicely.
If you're not into maths, Curve Builder will remain a complete mystery but if you want to better understand parametric functions, then it very easy to use.