Sage: Open Source Mathematics Software

Maxima GPL CAS based on DOE-MACSYMA   (Compare Project)

Mostly written in Lisp

License: gpl

Math::Symbolic   (Compare Project)

Mostly written in Perl

License: Artistic_License_2_0, GNU_General_Public_License_1_0, gpl

Atlas (Automatically Tuned Linear Algebra Software)   (Compare Project)

Mostly written in C

License: BSD-3-Clause

igraph library   (Compare Project)

Mostly written in C

License: gpl

DOLFIN   (Compare Project)

Mostly written in C++

License: lgpl3

Yacas   (Compare Project)

Mostly written in JavaScript

License: lgpl21_or_later

YAGY   (Compare Project)

Mostly written in JavaScript

License: GNU-GPLv2

Functy   (Compare Project)

Mostly written in C

License: mit

SpeedCrunch   (Compare Project)

License: gpl

Qalculate!   (Compare Project)

Mostly written in C++

License: gpl