As I want to reduce my webhosting and server accounts, I need a kind of gallery software written in PHP for my photos to replace Gallery2. I don’t like Gallery2, and it is big, needs a lot of memory and is damn slow. I collected some requirements I have (no hierarchical storage but tag/keyword based, fast, PHP, themable, no MySQL required, SQLite or flat file based, searchable, …) and I did not find any PHP gallery out there matching those. (If you have an idea, please tell me!)
So I started to write a generic system (second try, I have some nice ideas but the implementation lacks of some concrete content, a nice overhead, little more at the moment) to built a gallery on top of. And, what I did, too, was looking for existing PHP frameworks which could help me. There is a huge list of usable MVC frameworks on Wikipedia.