darktable is an open source photography workflow application and raw developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them.
Have a look at our current features and how to install it on your system.
darktable is created for photographers, by photographers.
Mention that having (photographer) developers as part of the target audience is good for understanding the real world problems, challenges, and workflows.
Something about capability - highlight about some big important features! Maybe mention flexibility here (ease of writing new modules).
Something about community, mailing list, maybe discuss forum, and the Flickr page? Number of contributors (indicate health of the project and users). Some other metric of vitality of the community (possibly how to get involved)?