A toolkit to work on PDF documents. From the page: "If PDF is electronic paper, then pdftk is an electronic staple-remover, hole-punch, binder, secret-decoder-ring, and X-Ray-glasses."
Mustajuuri (Black salsify, Scorzonera hispanica) is an audio signal processing application and toolkit. Written in C++. One of the targets of BlockCompiler.
BlockCompiler (BC) is an experimental programming environment particularly for time-domain modeling and simulation of physical systems, but it also has appropriate support for digital signal processing. BC was originally developed for physics-based modeling.
A nice page of the late Tony Fisher, has interactive tools to design analogue (LC, Butterworth and Chebyshev) and digital (IIR, including Bessel and an additional stopband zero and FIR) and PLL loop filters. The tool (source code is available) also gene
Cool page about (semi)numerical algorithm, including a book in progress, an open source library and a number of interesting links. Also has a mirror of hakmem. The author has also published a book about pi.