Pictures, along with their thumbnails, are stored in files, together. They can be organized in categories, through a database. I felt the need for such a software after I got my digital camera. This software is written in PHP for the web server side, and there is a perl client for managing the database. There is a mailing list for the photo project, and it is hosted by sourceforge.
Archives are available and can be found on the subscription page.
Sourceforge A big thanks to sourceforge for hosting this project. You can find the project page here .