I needed a simple gallery application for a client, and the PHP-based PhotoStack fit the bill.
Sure, the last time I looked at PhotoStack, I was concerned about the license, but it’s now GPL‘d.
I had to hack it just a bit to do what I needed, but it was fairly simple, involving minor changes to the photostack.class.php file, and then creating a custom theme. Kudos to Noel Jackson for making this nifty little open-source app available.