(E)2 Photo Gallery is an open source gallery built with Mootools Javascript Library the compact, modular, Object-Oriented javascript framework. Designed to allow you to upload your photos to a desired folder, tell the (E)2 Photo Gallery what folder to look at and it will automatically load the images using PHP. It looks very good and easy to use. You can customised it with different designed skins easily. However, currently it is not possible to have multiple galleries on one page.

Requirements: Mootools Javascript Library
Demo: http://www.e2interactive.com/e2_photo_gallery/demo.php
License: License Free