FLINT (Fast Library for Number Theory) is a C library in support of computations in number theory. It's also a research project into algorithms in number theory.
FLINT 2 is a complete rewrite of the FLINT library from scratch. It includes much cleaner code and in many cases much faster algorithms and implementations.
At this stage FLINT consists mainly of fast integer and polynomial arithmetic and linear algebra. In the future it is planned that FLINT will contain algorithms for algebraic number theory and other number theoretic functionality.