FFTW is a fast C FFT library. It includes complex, real, symmetric, multidimensional, and parallel transforms, and can handle arbitrary array sizes efficiently.It is typically faster than other freely available FFT implementations, and is even competitive with vendor-tuned libraries (benchmarks are available at the homepage). To achieve this performance, it uses novel code generation and runtime self optimization techniques (along with many other tricks).
FaCiLe is a constraint programming library over integer finite domain written in OCaml. It offers all usual facilities to create and manipulate finite domain variables, arithmetic expressions and constraints (possibly non-linear), built-in global constraints, and search goals. It also allows you to build easily user-defined constraints and goals (including recursive ones), making pervasive use of OCaml higher-order functionals to provide a simple and flexible interface for the user.