ODE is a high performance library for simulating rigid body dynamics. It is fully featured, stable, mature, and platform independent with an easy-to-use C/C++ API. It has advanced joint types and integrated collision detection with friction. ODE is useful for simulating vehicles, objects in virtual reality environments, and virtual creatures. It is currently used in many computer games, 3D authoring tools, and simulation tools.
Date::Calc::XS is a Perl module that is the C/XS part which Date::Calc used to consist of. Date::Calc has become a (pure-Perl) wrapper which tries to load Date::Calc::XS, and failing that, loads Date::Calc::PP (a pure-Perl implementation which is now part of Date::Calc and used to be Date::Pcalc).
CSpec is a behavior-driven development framework for C. It provides a spec framework for describing the behavior of the functions of your system. The syntax is inspired from RSpec to be as legible as possible. The source code is as portable and as light as possible to make it easy to run the library on embedded devices.
XSockets is an open, lightweight, and highly portable library of universal and extensible super sockets for point-to-point communication. It provides a unified API for many communication methods between programs and devices. Currently, many methods of point-to-point communication are well established, like TCP/IP sockets, serial links, named pipes, infrared, or Bluetooth connections. XSockets is meant to provide a single API that can be used for of these methods and more.
Gimp User Filter is a work-alike to Adobe's Filter Factory. It is a generic image processing plug-in that can be used to create new filters for The GIMP without having to go through the process of learning about The GIMP's SDK. Many freely available filters that have been created for Filter Factory can also be used with this plug-in.
MathGL is a library for making high-quality scientific graphics under Linux and Windows, fast data plotting and handling of large data arrays, working in window and console modes, and easily embedding into other programs. It has more than 40 general types of graphics for 1d, 2d, and 3d data arrays. It can export graphics to raster and vector (EPS or SVG) formats. It has an OpenGL interface and can be used from console programs. It has functions for data handling and MGL language scripting for simplification of data plotting. It has several types of transparency and smoothed lightning, vector fonts and TeX-like formula drawing, an arbitrary curvilinear coordinate system, and many other useful things.
gtkaml is an XML syntax and parser that extends the Vala.Parser and transforms all your tags into a valid Gtk+ UI class. It features a casual XML syntax for describing the way Gtk widgets are laid out in a (new) custom widget you're creating. Code "islands" (written in Vala) are used for widget signal handling and other methods/signals/properties that you're introducing. It doesn't depend on an external library at run-time, and it is much more readable than the usual UI boilerplate.