SageMath (formally known as SAGE) is free and open software that supports research and teaching in algebra, geometry, number theory, cryptography, etc. SAGE includes the following software: GAP, Maxima, Singular, PARI, MWRANK, NTL, Numeric, Python, IPython
Citation (https://wiki.sagemath.org/Publications_using_SAGE):
@manual{SAGE,
key = {SageMath},
author = {The Sage Developers},
title = {{S}ageMath, the {S}age {M}athematics {S}oftware {S}ystem ({V}ersion x.y.z)},
note = {{\tt http://www.sagemath.org}},
year = {YYYY},
}