Mathematics

• BLAS (Basic Linear Algebra Subprograms) link (public domain)
• LAPACK -- Linear Algebra PACKage link (public domain)
• ATLAS Automatically Tuned Linear Algebra Software link (BSD license)
• Meschach: Matrix computations in C link (GPL? license)
• GSL: Gnu Scientific Library link (GPL)
• FFTW "Fastest Fourier Transform in the West." link (dual license GPL/commercial)
• KISS-FFT "Keep It Simple, Stupid." Fourier Transform link (include copyright note)
• Algorithmic C Fixed-point datatypes (Mentor Graphics) link (proprietary)

Image Processing

• OpenCV library of aimed at real time computer vision link (BSD license)
• IVT (Integrating Vision Toolkit) camera model, image processing, optional GUI binding link (GPL)
• GDAL Geospatial Data Abstraction Library link (X11/MIT license)
• Vigra "Vision with Generic Algorithms" link (X11/MIT license)
• Cimg C++ template image processing toolkit link (CeCILL)
• Corona Image import/export link zlib/libpng License
• Imlib Inport/export; X11 rendering, ... link (GPL)
• Imlib3D C++ library for 3D (volumetric) image processing link (GPL)
• CVL library for image and data processing using GPU link (GPL)
• libCVD computer vision library link (LGPL)
• Olena generic library for image processing link (GPL)
• GMIC convert, manipulate and visualize generic 1D/2D/3D multi-spectral image datasets link (CeCILL)
• Blepo computer vision C/C++ library link (GPL)