It isn't alternative to photoshop though, what about darktable (https://www.darktable.org/)? I could be wrong but it is more of an alternative to lightroom afaik. Have you used?
Thanks for the suggestion. I've never been really into the "catalog" apps, starting from itunes. Always been more of a winamp guy ;) I like to browse my files from the explorer and not having to deal with a software to navigate or a software to catalog files and corrupting my filetree.
I've been using gimp since one week and so far, once you start trying to understand what's going on (something I never allowed it since 20 years I've tried), it's really not that bad.
Darktable may have a catalog, but like you, I've never seen the value in that. It's primary purpose is as a RAW editor, and it's pretty good at that. Highly recommend it as a first pass for any digital photography. That, or Rawtherapee.
I've been using gimp since one week and so far, once you start trying to understand what's going on (something I never allowed it since 20 years I've tried), it's really not that bad.