libposix is an impementation of the core functionality of all Unix systems. It is a full, cross-platform implementation of the POSIX 2008 standard. It is meant to replace existing implementations of a Unix system's core libraries. It is an exact implementation of POSIX 2008 and nothing else (no extensions, no previous POSIX versions). However, it works well with possible extensions to the core system functionallity (for example, GNU or BSD).
Huxley is a set of classes that makes it trivial to produce legitimate output for queries made by the prevailing standard of REST queries. Instead of writing a network API with many methods, being run over RPC, you instead write only a couple of methods that are accessed by HTTP GET requests. You then return the results (in either XML, JSON, or text) for processing. XML and JSON are chosen because of the ease by which they can be parsed by most languages. In this way, you open up the scope of your network services to many more people than would otherwise have access to it.
jCores is a Java library that feels like jQuery, with many shortcuts and transparent parallelism. It was made to denoise programming in the Java language and to increase execution speed. Its goal is to demonstrate that Java, the language, can be as sexy as Python in terms of hacking and as parallel as your hardware gets in terms of CPUs.
Libpointmatcher is a modular "Iterative Closest Point" library, useful for robotics and computer vision. This library is designed with modularity and performance in mind. It provides building blocks to construct various ICP chains often seen in research. These chains can be tuned without any recompilation, and new modules can be added without modifying the core of the library.
Biomechanical ToolKit (BTK) is a cross-platform library for biomechanical analysis. It can read and write a large variety of file formats used in biomechanics, and can modify them. All these operations can be done with the C++ API or with the wrappers included (Python, Octave, and Matlab). The goal of this project is to help the community share data without the restriction of the file format or the biomecanical model provided by the manufacturer of the acquisition system.
LibU is a multiplatform C library that comes under a BSD-style license. It includes many interdependent modules for accomplishing several tasks: memory allocation, networking and URI parsing, string manipulation, debugging, and logging in a very compact way, plus many other miscellaneous tasks. It has a small footprint (about 70KB for the default configuration), it is modular, and it has a multiplatform nature, making it an ideal candidate for embedded systems. KLone is an example of such usage.