Open Source Solid Modeling CAD
BRL-CAD is a powerful cross-platform constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing for rendering & geometric analyses, network distributed framebuffer support, image & signal-processing tools.
Realtime audio synthesis library using the flexible unit generator architechture. Many uses: music, scientific sonification, generic audio processing. Multithread abilities, extensible synth framework. Similar to modular analog synths.
QXi, the Qt XInput extension, is a library to add support for XInput devices (e.g. tablets) to Qt-based applications. It's currently in early development. The library is built using autoconf and comes with example applications. Requires Qt2.1 or newer.