PFFFT is a very small 1D Fast Fourier Transform library based on the venerable FFTPACK v4. It handles single precision real and complex transforms. Computations take advantage of SSE1 instructions on x86, Altivec on PowerPC, and NEON on ARM, allowing it to achieve a performance level that is not too far from the very best FFTs (FFTW, Intel MKL, Apple vDSP).
SLEEF (SIMD Library for Evaluating Elementary Functions) is a library that facilitates programming with SIMD instructions. It implements the trigonometric functions, inverse trigonometric functions, exponential and logarithmic functions in double precision without table look-ups, scattering from, or gathering into SIMD registers, or conditional branches. This library also includes some functions for evaluation in single precision.
Orc is a library and set of tools for compiling and executing very simple programs that operate on arrays of data. The "language" is a generic assembly language that represents many of the features available in SIMD architectures, including saturated addition and subtraction, and many arithmetic operations.
NSFFT is yet another FFT library for performing 1-dimensional fast Fourier transforms. It is a simple, small, and portable library, and it is efficient since it can utilize SIMD instruction sets in modern processors. It performs multiple transforms simultaneously, and thus it is especially suitable for digital signal processing.