Maxima is an active open source project or the manipulation of symbolic and numerical expressions.
Citation:
@Article{maxima,
author = {Joyner, David},
title = {OSCAS: Maxima},
journal = {ACM Commun. Comput. Algebra},
issue_date = {September-December 2006},
volume = {40},
number = {3-4},
year = {2006},
issn = {1932-2240},
pages = {108--111},
numpages = {4},
url = {http://doi.acm.org/10.1145/1279721.1279726},
doi = {10.1145/1279721.1279726},
publisher = {ACM}
}