PARI/GP is a widely used computer algebra system designed for fast
computations in number theory (factorizations, algebraic number theory,
elliptic curves...), but also contains a large number of other useful
functions to compute with mathematical entities such as matrices,
polynomials, power series, algebraic numbers, etc., and a lot of
transcendental functions. PARI is also available as a C library to allow
for faster computations.