There Internet is replete with sites and services offering to let you organize, manage, and share your digital photographs and Yahoo's Flickr remains an undisputed leader in the field. Partly, that's because Flicker offers easy-to-use features and boasts and enormous, active, and tremendously engaged user community. But it's also because Flickr has had the foresight to let third-party developers build their own add-ons and supplementary services using Flickr's data and images. Geeks, programmers, and photo buffs have embraced Flickr's open APIs enthusiastically, so even if Flickr doesn't offer a feature you want—or its features aren't up to your task—odds are good a third-party solution already exists to solve the problem for you. So, if you're using Flickr and wondering how you can get more out of it, here's a quick introduction to some tools and services—from the cool to the geeky—which can expand your Flickr universe.