Chebfuns (google it..) are about Chebyshev approximations to functions,
and are fun.
You can read about this topic with relationship to Maxima,
in a newly revised paper at
http://www.cs.berkeley.edu/~fateman/papers/cheby.pdf
and all the relevant programs and some irrelevant ones are here:
http://www.cs.berkeley.edu/~fateman/cheby
Comments, suggestions, questions, etc welcome.
(I suspect I emailed to this list about this topic, but an archive
search doesn't find it... Anyway the paper is a little cleaner now,
as are the programs. )
RJF