I have used Darktable on both Linux and OS X. There is no Windows version. It works well, but does have a learning curve to it, as does most photo software. If you are running OS X, I think it is a good alternative to Lightroom, especially if you do not like Adobe's new subscription practice (please, no spears and arrows from those who have no issue with the subscription model for software). Darktable has a lot of features, more than what the article discusses. It is definitely worth a look if you are running OS X. If you are running Linux, it is a very viable option. I like it a lot better than RawTherapee, which I found rather clunky and slow.
Thanks for posting the article and letting people know there are alternatives to Lightroom.