The free, open source, editor darktable image, comes as a very good alternative to Lightroom for Windows. And of course it runs on all other Linux and Mac platforms.
If you are looking for a free alternative to manage and processing image software like Lightroom, there is some good news: free and open source software darktable has reached version 3.4.1 (for Linux) and is finally available for Windows users as well.
The darktable originally released in 2009, it has been used by professional photographers on Mac and Linux operating systems. The software includes a set of features exwork photo editor that helps you edit RAW files, especially large sizes.
After some timid attempts with version 3.2.0, darktable has now been officially transferred to operating system Windows (64-bit only), in this new edition of 3.4.0, and as its developers state in their announcement, they intend to support it in the future.
In addition to Windows support, 3.4.0 brings a series of new changes, features, bug fixes, and camera support. You can find the entire list of changes and improvements to company announcement.
You can download it darktable 3.4.0 from here, where you will also find the new 61.5MB download entitled "darktable-3.4.0-win64.exe" for Windows.