Computer Algebra SystemsMy hobby is a symbolic manipulation programming. I don't like the language and the whole philosophy behind Maple/Mathematica and I think it could be done better, so I started SymPy, which is a symbolic manipulation package, written in Python. The aim is to have a full featured CAS in Python, but also to have the code as simple as possible so that it can be easily learned and extended. Many other very good developers has joined the development, so things look promising. See that link for more info. I am not the only one with this opinion, recently it's the Sage project (that also includes SymPy among other symbolic libraries), that directly aims to create an open source alternative to Maple/Mathematica/Matlab, together with a GUI (notebook in a browser). In November 2007, I attended the Sage Days 6 workshop (see my notes describing my overall impressions from that) and in March 2008 I attended the Sage Days 8 workshop (impressions).
I also created python bindings to GiNaC in SWIG together with Ola Skavhaug, our project is called swiginac.