Ansible is a radically simple deployment, configuration, and command execution framework. It is dead simple and painless to extend. Extending Ansible does not require programming in any particular language; you can write modules as scripts or programs which return simple JSON. It’s also trivially easy to just execute useful shell commands.
ccglue is a complementary tool to cscope and ctags. The tool builds a cross-reference symbol database from cscope (and ctags) databases that can be used to display dependency-graphs (aka call-trees, code flow). Visualization can be done with the Vim CCTree plugin or the built-in stand-alone command-line tracer.
Upmf is a source-based package manager written almost completely in Scheme. The user is able to search, build, and remove packages. Since Scheme through GUILE is very extensible, the user can customize the procedures, or even exchange them with his own, if wanted. Packages are stored in their own self-contained directories and are incorporated into the filesystem with help of GNU Stow.
The minfx project is a Python package for numerical optimization. It provides a large collection of standard minimization algorithms, including the line search methods (steepest descent, back-and-forth coordinate descent, quasi-Newton BFGS, Newton, and Newton-CG), the trust-region methods (Cauchy point, dogleg, CG-Steihaug, and exact trust region), the conjugate gradient methods (Fletcher-Reeves, Polak-Ribiere, Polak-Ribiere +, and Hestenes-Stiefel), the miscellaneous methods (Grid search, Simplex, and Levenberg-Marquardt), and the augmented function constraint algorithms (logarithmic barrier and method of multipliers).
Zutils is a collection of utilities able to deal with any combination of compressed and uncompressed files transparently. If any given file, including standard input, is compressed, its decompressed content is used. Compressed files are decompressed on the fly; no temporary files are created. These utilities are not wrapper scripts but safer and more efficient C++ programs. In particular the "--recursive" option is very efficient in those utilities supporting it. The provided utilities are zcat, zcmp, zdiff, zgrep, ztest, and zupdate. The supported formats are bzip2, gzip, lzip, and xz. The compressor to be used for each format is configurable at runtime.
The GNU Autoconf Archive is a collection of more than 450 macros for GNU Autoconf. They can be re-used without imposing any restrictions on the licensing of the generated configure script. In particular, it is possible to use them in configure scripts that are meant for non-free software.