GEOS (Geometry Engine - Open Source) is a C++ port of the Java Topology Suite (JTS). As such, it aims to contain the complete functionality of JTS in C++. This includes all the OpenGIS "Simple Features for SQL" spatial predicate functions and spatial operators, as well as specific JTS topology functions such as IsValid()....

UFO: Alien Invasion is a strategy game featuring tactical combat against hostile alien forces which are about to infiltrate earth at this very moment. You are in command of a small special unit which has been founded to face the alien strike force. To be successful on the long run, you will also have to have a research team study the aliens and their technologies in order to learn as much as possible about their technology, their goals and the aliens themselves....

VisualBoyAdvance is a GameBoyAdvance emulator. It's not the fastest but it aims to be the most accurate.

Crystal Space is a free, cross-platform software development kit for realtime 3D graphics.
It supports Windows, Linux, MaxOS/X and more. Though written in C++, other languages like Python can also be used to write programs.
Based on a plugin system it's very modular and extended easily. ...

Arcemu is a World of Warcraft server package. Based on the popular Ascent project it aims to provide players with a gameplay very close or identical to the real thing.

It's a multithreaded C++ application with a relational database as a data storage backend( mysql and postgresql are the only supported ones this time)....

Sauerbraten (a.k.a. Cube 2) is a free multiplayer/singleplayer first person shooter, built as a major redesign of the Cube FPS.

KMyMoney is the Personal Finance Manager for KDE.
It operates similar to MS-Money and Quicken, supports different account types, categorisation of expenses, QIF import/export, multiple currencies and initial online banking support.

gv allows to view and navigate through PostScript and PDF documents on an X display by providing a user interface for the ghostscript interpreter.

CppUnit is the C++ port of the famous JUnit framework for unit testing. Test output is in XML for automatic testing and GUI-based for supervised tests.

GNU DDD, the Data Display Debugger, is a GUI to command-line debuggers like GDB, DBX, JDB, XDB, Ladebug, WDB, the Perl debugger, or the Python debugger. It provides a graphical data display where complex data structures can be explored incrementally and interactively....