SAGE is an open source mathematics software, which is developed by some teams, including core arithematic, 3D Graphics, group theory, graph theory implementation, GSL, coding theory, and others. The core arithematic team includes David Harvey (a graduate student in number theory at Harvard University), Martin Albrecht, Joel Mohler, Robert Bradshaw, William Stein (an associate Professor of Mathematics, University of Washington).
By using SAGE you help to support a viable open source alternative to Magma, Maple, Mathematica, and MATLAB. SAGE includes many high-quality open source math packages.
SAGE makes it easy for you to use most mathematics software together. SAGE includes interfaces to Magma, Maple, Mathematica, MATLAB, and MuPAD, and the free programs Axiom, GAP, GP/PARI, Macaulay2, Maxima, Octave, and Singular.
(The information is from http://www.sagemath.org)