Joe Strout: > to find anything that's quite what I'm looking for. I'm aware of these: > > http://web.usna.navy.mil/~wdj/opensource_math.html > > ...but none of them sound as general and powerful as Mathematica. > Maxima sounds close, though it's actually a predecessor of Mathematica;
I find Maxima, along with wxMaxima as a front-end sometimes, works just fine for what I use it for. Having "grown up" using Macsyma probably helps. What, in particular, did you have in mind?
If you don't find any of the listed projects powerful enough, perhaps you could consider contributing to one of them, such as Maxima. Open source doesn't grow without attention.