One of the biggest projects, which I crafted alone, was a platform for renting out real estates. The first version was quickly made in a few weeks, called mietenkaufen.at. Superseeded by a second version, multi lingual, multi category, featuring "remember ads" functions, video uploads, nice galleries and many more. It was from the beginning on enterly free of charge. At the time of creation not a lot of competition was on the market and what was there, was not really good.
The website was written in PHP on the backend side and HTML/JS on the Frontend.
Find more information on http://www.mietenkaufen.net