Libcwd is a full-featured and well-documented library that assists C++ developers with debugging their applications. It includes support for ostream-based debug output, custom debug channels and devices, memory allocation debugging, run-time sourcefile:linenumber information, and demangled type names of variables. It is thread-safe.
Eckbox is van Eck Phreaking tool that interprets a radio signal emanating from a computer's monitor to recreate the image (in black and white) that is displayed on it. It could be used as a valuable security tool for testing otherwise secure computers or for developing hardware and software to counter this type of remote shoulder-surfing. It is not intended to be used for illegal purposes, and includes information on the hardware required.
Ivman is a flexible userspace volume manager for Linux. Originally an automounter, it can also be used to run arbitrary commands when certain devices are added to or removed from the system, when properties on existing devices change, or when devices emit conditions. Unlike gnome-volume-manager, it runs from a console. It uses D-BUS and HAL to listen for new devices, and uses pmount for mounting.
The Qt XInput Extension is a C library adding support for XInput devices (like tablets or joysticks) to Qt-based X11 applications. QXi supports devices with up to six valuator axes in absolute mode, up to 32 buttons, and any number of keys. It is built using autoconf and libtool, and comes with a simple example application.