Qt is a comprehensive, object-oriented development framework that enables development of high-performance, cross-platform rich-client and server-side applications. When you implement a program with Qt, you can run it on the X Window System (Unix/X11), Apple Mac OS X, and Microsoft Windows NT/9x/2000/XP by simply compiling the source code for the platform you want. Qt is the basis for the KDE desktop environment, and is also used in numerous commercial applications such as Google Earth, Skype for Linux, and Adobe Photoshop Elements.
Dimenso is a library for performing dimension-aware calculations in C# and Java. It offers numeric types that have dimensions, expressed in terms of base dimensions M (mass), L (length), T (time), and Q (electric charge). Playing to the strengths of each language, C# types have operator overloads to allow them to be used as numbers, while Java types mimic the BigDecimal with respect to arithmetic methods.
nCore is an efficient and portable C++ library for developers. It includes a set of several satellite C++ classes to perform threading, file I/O (with endian-awareness), networking (TCP, UDP, IPv4, and IPv6), high-perf timing, easy logging with pluggable sinks, memory allocation debugging, hashing (MD5, string, CRC32, CRC16, and CRC8), loading of dynamic libraries (shared objects), dog-tagging (your final application/library binary file(s)), handling wide string manipulation methods through a single class (StringA), and more. Each of those features can be turned off at compile-time to make the final binary file smaller.
PBL (The Program Base Library) is a C library of array/linked list, hash/tree set, and key file functions that can be used in a C or C++ project. It is highly portable and compiles warning-free on Linux gcc, Windows Cygwin gcc, Mac OS X, and Windows Microsoft Visual C++ 2008 Express Edition.