LightZone

Lightzone, a commercial software, is a pretty good alternative for Adobe Lightroom. It can convert RAW files into simpler formats. It comes with a clean and stylish interface with a dark theme, which is essentially what made it popular among the image editing apps. The software interface is split into two distinct sections - a browse window for navigating through the files in your system and an editing window which enables the user to work on images in a specific area. LightZone is a pro-level photo editor software which provides a comprehensive editing experience by handing full control access to the user. The set-up is relatively intuitive for newbies as well. Unlike other software though, it doesn't allow sharing through email or other methods, as it saves files to the system organizer.

Why you must get it?
The main reason to get LightZone is that it is a complete package. It has features such as converting RAW images, and a wide array of commonly used image editing tools. Though it is an open-source project, it become a commercial tool these days with its comprehensive and detailed help files 
structure which is absent on some other popular photo editing software.