Ember is a great image cataloging app, and works much like its predecessor, LittleSnapper. You can import images from any source, and it is especially capable of pulling complete web pages - a great feature for web developers, website reviewers, and others. You can take images with various types of meta data, from which you can build smart albums. It has basic image annotation abilities, which remain fully editable. You can also use it to subscribe to image RSS feeds. Another handy feature is that you can sync libraries in the cloud.
