Open Tool Kit (Otk) is a portable widget library for making graphical user interfaces for C programs. It emphasizes simplicity for the application programmer without eliminating capability. Based on OpenGL, Otk supports Linux, Unix, and other OSs neutrally and efficiently. It is simple and compact, and it strives for easy compilation and linking to other applications. In seeking to address several issues associated with earlier graphics APIs, Otk explores some interesting methods, such as window-relative layout instead of pixel-based layout.
Mapnik is a toolkit for developing GIS applications. At the core is a C++ shared library providing algorithms/patterns for spatial data access and visualization. Essentially a collection of geographic objects (map, layer, datasource, feature, and geometry), the library doesn't rely on "windowing systems" and can be deployed in any server environment. It is intended to play fair in a multi-threaded environment and is aimed primarily, but not exclusively, at Web-based development. High-level Python bindings (boost.python) facilitate rapid application development, targeting zope3, django, etc.
Mathomatic is a portable, general-purpose computer algebra system (CAS) that can solve, differentiate, simplify, combine, and compare algebraic equations, perform standard, complex number, modular, and polynomial arithmetic, etc. It does some calculus and is very easy to compile/install, learn, and use. The symbolic math application with a simple command-line interface is designed to be a colorful algebra calculator that is reliable, responsive, and convenient to use. The symbolic math library is lightweight and easy to include in other software, due to being written entirely in C with no additional dependencies.
ff3sudoku is an add-on that features an engine for playing Sudoku puzzles. It can generate random puzzles, but it also detects and imports Sudokus from several Web sites, including websudoku.com, sudokupuzz.com, sudoku.com.au, and others. There is also a stand-alone version working in Firefox 3+ and GoogleChrome.
The HOTP Toolkit package contains tools that are useful when deploying the one-time password HOTP technology. It contains a shared library, a command-line tool to generate and validate one-time passwords, and a PAM module (pam_hotp) to make system login or SSH use HOTP one-time passwords for authentication.
The stx::CBTreeDB is a collection of C++ classes with which read-only key-value database files can be created and read. A database efficiently maps a large number of integral fixed-length keys to opaque binary value blobs. Variable-length or duplicate keys are currently not supported. Keys are organized into a highly compact index structure, which is very similar to a B-tree and allows very fast key lookups. Both keys and values are stored in order and thus queries in a local proximity can benefit from caching effects. All applications mapping a large number of constant, integral keys to string or data blobs can benefit from this library.