The free, open source, darktable image editor comes as a great alternative to Lightroom for Windows. And of course it runs on all other Windows, Linux and Mac platforms.
If you are looking for a free alternative to image management and editing such as Lightroom, there are some good news: free and open source software darktable has reached version 4.0 (for Linux) and is finally available for Windows users as well.
The darktable was originally released by 2009 and has been used by professional photographers on Mac and Linux operating systems. The software includes a set of photo editing capabilities that helps you edit RAW files, especially in large sizes.
After some timid attempts since version 3.2.0, darktable has now been officially ported to Windows (64-bit only).
Version 4.0 brings a number of new changes, features, bug fixes, and camera support. You can find the full list of changes and improvements in company announcement.
You can download it darktable 4.2 from here, where you will also find the new 61.5MB download entitled "darktable-4.2.0-win64.exe" for Windows.