Otherwise, I know Maxima, which is quite alike, and free.
In both cases, you have to learn the syntax, what to type, etc... This is, imho, the most delightful (irony) part of these programs ^^
Concerning geometry you can use Geogebra. I can't tell much about it because I installed it only few weeks ago. But it's used in some high schools in France (if you want a reference).
Google will give you the links =)
Hope it helps.