darktable

Using purely Linux and getting deeper into photography I was looking for an application to manage my collection of raws and to develop them. After starting of with RawTherapee and having a short try with digikam I soon switched over to darktable. And I can say I never regretted it.
Out of my view it is a professional grade software, and beginners are advised to read the very comprehensive manual carefully while starting off with it. The manual is also a good source of reference. In addition there are many helpful video tutorials.
The developers put a big thought in image manipulating quality and often there is some serious science behind it. They for sure know their stuff, providing the best tools and algorithms for the task. The photo database management capabilities on the other hand still show some room for improvement. In general although the software is mature and ready to use there are regular releases with new features.
To summarize, darktable is a great tool to manage and develop your raw images in excellent quality. The learning curve gets easier by consulting the manual.