VisualMaths is a 2D curve drawing program (3D and dynamic curves not yet available). User defines objects (functions,variables,arrays) and assign each object to a curve and an axis. VisualMaths also provides some graphic solvers : minima, maxima.
ThreeSpace is a 3D drawing program, or modeller if you will, primarily intended for visualizing and playing with mathematical functions. It allows you to superimpose these or otherwise alter objects in 3D using them.