Many moons ago I needed a way of storing documents online, so they could be shared between users and easily accessed from many locations. Thus, Simple Document Management System was born. SDMS is a PHP based front-end to a MySQL database that allows users to upload and download files into and from virtual directories using only a web browser.
It was my second ever PHP project and I wrote it in (bad) php3, with only some informal C coding as experience. Needless to say the code was not great, it used globals and had SQL injection problems. Though I did fix these two particular issues, the code is still old and tired and I've not really maintained it for years. Bringing it up to date would probably involve more effort than just scrapping it and rewriting it from scratch.
I've been doing a lot of work with Drupal over the past year and I had been vaguely considering reimplementing SDMS as a Drupal module, thus removing the need for me to also maintain code to handle users, passwords, commenting and permissions.
As I got more familiar with some 3rd party Drupal modules, it struck me that it should be completely possible to implement a document management system similar to SDMS in Drupal. Without doing any coding whatsoever. Thus, SDDMS was born.