tmphoto is a Web photo gallery with a fairly advanced metadata structure, allowing photos to be described in terms of place, category, persons in the photo, and events. The places, categories, persons, and events can be further described. It offers a nice browsing interface based on the metadata.
Ontopia is a set of tools for building applications driven by Topic Maps, such as Web portals. The main benefit of Topic Maps is that they provide a flexible and expressive data model supporting much better findability than traditional solutions, as well as advanced features like automated merging of datasets.