I've got one exam to study for, and it happens to be about differential equations. It's always a good thing for me to find a computer program that aids learning. This time I was lucky: Maxima. Portage contains also a package with maxima mode for Emacs and a plugin that uses TeX to visualise the Maxima's output.
This software reminds me of Derive, a DOS program which could do calculus. I used it in the middle school to learn math, it helped me a lot. I hope Maxima will do so as well.