these are not open source, but I found them invaluable in helping visualize equations in an intuitive manner. For 2d use
GrafEq, and for 3d
DPgraph. They are both amazingly intuitive tools, and complement each other rather nicely. You should check if the college has licenses for the last one.
Another useful tool maybe Maple, again, if the college has the proper license. The lastest version has a number of "tutors" geared toward the first years of college (meaning calc I-III, and lin. alg.). There is a step by step symbolic integrator, for instance.
Anyway, my advice would be using tools that help creativity and visualization, not tools that do their work for them. And like other people have said, if they know a language like python or c++, they might be motivated to use it as a "playground" to explore ideas. This is very cool.