I was working at Mecca Bingo when Electronic Bingo Terminals were introduced. A clever form of sales discounts came with them, whereby an increasing number of free tickets would be given based on how many tickets were purchased on these terminals. Unfortunately this quickly led to issues; sales staff were required to calculate the number of free tickets by hand in order to calculate prize money for each game. This meant that somebody could be spending anything up to an hour every day messing around with a calculator and notepad rather than doing their jobs. And the number of errors caused by rushing somebody with a calculator and notepad were uncountable, leading to more time wasted as administration staff found and corrected them.

Enter myself, a copy of GCC and my favourite keyboard. The EBT Sales Assistant reduced the entire calculation process to four clicks and drastically reduced the risk of human error.
The EBingo Sales Helper was written in C, using GTK+ for the GUI. I had already been using GTK+ to create a few other tools for my own use, and the time-to-live using Glade was exceptionally short.

Development and testing was a dynamic affair, with the software being modified day-to-day as it was tested live. It quickly became able to handle everything that was thrown at it, and remained in use for almost two years before a complete system replacement, saving literally hundreds of hours in its operational lifetime.