Open Source Photo Gallery: GMFoto
GMFoto is an open source photo gallery script, built with PHP & does not require a database.
With the template & multi-user support, the script offers a wide-usage from a single installation.
Images can be added by uploading via FTP or with KFM. They will be compressed and resized automatically.
GMFoto provides an unlimited category logic which can be created when uploading images as every folder is a category.
Images are displayed in a Lightbox and can be browsed easily with prev-next buttons.
Although the script is in early beta, it is a very promising one.