Indielib is a C++ 2.5d library for game development and fast game prototyping in a really easy way. It was originally written for DirectX 9.0c. This project is the cross platform version of this library.
Platforms

Windows
    Linux
    OSX
    iOS

Renderers...

Youki is the current media player produced by the MediaPlayerExperiments team: youki is a very simple, powerful and very fast media player.

KMuddy is a MUD client powered by KDE. It aims to be the most powerful, fast, feature-rich and easy to use MUD client.

The current version already offers many features such as powerful external scripting (which supports very many languages such as Python, Perl, Lua, C/C++), and it's own internal scripting. It has split-screen scrolling, command history, buttons, gauges, logging (both in plain text and HTML), multiple connections, regex support (on both aliases and triggers)....

ORCA is an interpreter for a REBOL-like language. The interpreter is a C library so that C/C++ applications can use ORCA as an embedded scripting system. ORCA stands for Open-source Rebol Can be Achieved.

PDF Cube uses Poppler and OpenGL APIs to add 3D spinning cube page transitions to PDF documents.

PDF Cube is a tiny (~28KiB) program to render PDF presentations with special 3D effects (a rotating cube and 5 predefined zoom animations). It adds eye-candy to your PDF presentations, even Latex, Beamer and Prosper ones....

Isometric client/server based MMORPG Featuring: 2d+ (isometric mapstacking), tilestretching (looks 3d) and realtime map editing. Linux (source) and Windows (.exe) versions are available. Uses SDL graphics library for portability. Alpha 2 in development.

The dANN project is a library to help facilitate artificial neural networks within other applications. It is currently written in Java, C++, and C#. However only the java version is currently in active development. If you want to obtain a version other than the java version you will need to get it directly from GIT....

Qfusion is a game engine based on sources from Quake II code. It is available for download and modification for free under the GNU General Public License (GPL). Qfusion has helped to set the bar for many other Quake II engine projects. A popular feature of the engine is that it is said to be able to correctly render the entire range of content for Quake III....

profilHub is a hub of debugging and profiling tools for Linux.

It aims to gather useful existing profilers and analyzing tools into one beautiful place, in order to help C and C++ developers to check the stability and to enhance the performances of their code in fast, intuitive and interactive ways....

emerge is an alternate windows shell. It's purpose is to replace Windows Explorer as your desktop user interface, providing similar functionality, with the additional plugins to provide even more.