QMentat helps you practice mental arithmetic. It uses arbitrary-length fixed point arithmetic, and can handle any size numbers, only limited by the size of your screen (and in the case of division with an integer result, the speed at which the number can be factored). It is also quite configurable, allowing you to tailor the questions to your needs.
libjmmcg is a basic, low-level library with pretensions to implementing features above and beyond (but not necessarily better than!) those implemented within the Standard C++ Library and the Boost Library. It features a library for multi-core or multi-chip SMP parallelism, a suite of hashing algorithms, functions for raising numbers to integer powers, a generic factory wrapper and a generic, multi-threaded, read-only cache (which uses PPD), arguably the world's worst sorting technique, trace output, exceptions that have the file, line, revision, function, and argument details, string utilities, logging, simple command line processing, and much more.
Government Sanctioned is a custom-developed text-based RPG (i.e., MUD). New players enter the world of Government Sanctioned as covert agents working for a super-secretive government organization colloquially known as "the agency". Players have a choice of six different roles spanning 19 unique professions. Whether you like stealthy, clandestine operations, the use of subterfuge and guile to infiltrate enemy organizations, or full-blown military actions, the agency has a spot for you. Players are empowered to deeply customize their character through numerous differentiation mechanisms. Character backgrounds lay the foundation for character abilities and are further defined through their cover occupation and agency department affiliation. To put a fine point on character customization, the skill and feat system provides an extensive array of options to tweak the character to suit your style of game play. The skill system boasts over 35 different skill families with around 50 different skills and checks. Skill points are gained upon professional level advancement and can be spent any way the player chooses. With 19 feat trees and over a hundred diverse feats (with new feats being added regularly), your capability for customization is endless.
libktomgirl is a library that reads a subset of the Tomboy file format. When it's done, it should support reading and writing all aspects of files created by Tomboy, Gnote, and KTomGirl. Despite the K in its name, there are no KDE or Qt dependencies (nor C#, GKT, or GLIB). This is pure C++ with boost and stdlib only. Most of the code is from Gnote.