A few years ago I bought a guitar effect, USB-sound-card like device - thinking the support for it will be easy to do in linux... Long story short - it wasn't.
A friend of mine allowed me to use his pebble watch for a few months, to decide whether wearables are for me... A good opportunity to code a few apps :)
A home alarm written in python, which uses RFID for authentication, can capture/send pictures via webcam, activate alarm via GPIO.
Driver for a fingerprint sensor - vfs301 usb device 138a:0005. Reportedly it also works for 138a:0008 (vfs300), and maybe also other compatible ones...
A simple tool (written in Mono/Qyoto) for calibrating maps (mainly) for PocketGPS-Map. Also a tech-demo of how to use Qt in C#. It is licensed under GPLv3 (or later).
This program views calibrated bitmap maps on PocketPC (WinCE) platform. Additionaly it supports using GPS device to retrieve user position and show it (with other marks) in map - making it very handy for geocaching.
Another Racing Simulator
Mines game written in Qt3
Mines game written in Java
A win32 logical game for 2 players