Here is various software on which I work. Some of it are just quick implementations of some missing functionality, but there are also big projects like phpMyAdmin or Gammu.
Software for managing mobile phones and creating SMS gateway. Gammu is the name of the project as well as name of command line utility, which you can use to control your phone. It is written in C and built on top of libGammu.
Gammu SMSD: http://wammu.eu/smsd/
Wammu is a program to manage data in your cell phone such as contacts, calendar or messages. It is built on Gammu library, which provides abstraction layer to work with different cell phones from different vendors (including Nokia, Sony-Ericsson, Motorola, Samsung, Siemens, Huawei and others).
phpMyAdmin is a free software tool written in PHP intended to handle the administration of MySQL over the World Wide Web. phpMyAdmin supports a wide range of operations with MySQL. The most frequently used operations are supported by the user interface (managing databases, tables, fields, relations, indexes, users, permissions, etc), while you still have the ability to directly execute any SQL statement.
Demo server: http://demo.phpmyadmin.net/
Daily snapshots: /software/phpmyadmin/
Weblate is web based translation tool with tight Git integration. It features simple and clean user interface, propagation of translations across subprojects or automatic linking to source files.
Demo server: http://demo.weblate.org/
I am a Debian Developer and you can find here various packages for Debian.
As I like StarDict much, I decided to hack scripts that will convert some useful dictionaries to it's format.
Various GPS and compass based tools for Nokia N9 (Harmattan).
Simple tool in Qt Quick to calculate depth of field for photographers for Nokia N9 (Harmattan)..
Simple todo application using PHP and MySQL. It does not provide user authentication, only simple task sorting into categories and personal/work issues. It automatically detects links and formats text of entries.
Enca is an Extremely Naive Charset Analyser. It detects character set and encoding of text files and can also convert them to other encodings using either a built-in converter or external libraries and tools like libiconv, librecode, or cstocs.
Simple IMAP utilities written in Python.
Simple application to upload photos to minilab.
Charset conversion program for Windows.
Tool for displaying directory listing in PHP pages.
Simple polling daemon.
Web site system written in PHP.
Shell scripts for managing Diva MP3 player.
Simple monitoring modules gor HotSaNIC
KAlcatel is program for KDE to manage Alcatel 50x or 70x phone (only 501 is currently tested). It is known to work on Linux, but as well it may work anywhere where KDE 3.x work.
Command line utility and library to work with Alcatel phones.
Utility for shutting down, rebooting, hibernating and suspending computer and logging of user.