Hugin ( http://hugin.sourceforge.net/ ) can create brilliant panoramas, even from a bad batch.
Note: there is still no alternative to PS, given it's both a raster and a vector editor.
What's meant by bitmap in contrast to raster? In the context of graphics, I regularly use them as synonyms.
If the audience is casual editing (ie. a short time to improve a photo, and little user skills), I think Lightroom is significantly ahead of the competition - in particular, UX has never been a strong point of open source software.
I don't know if the latest years changed the landscape, but I suppose not - Adobe kept enhancing Lightroom.
License wise... that's definitely another story (I personally preferred when a license was valid for a single major version).
It is like comparing Gimp to Photoshop. Yes, they can do some of it, but they can't do it better or even close to that if you are serious at what you do.
I am a developer, I have been Linux user for years and photography is my hobby. I periodically try some Lightroom "alternatives" in hopes of finding something good, but they are still nowhere near of replacing it. And with the limited budget they will probably never be as good.
I know only one great open source software example in the arts field, and that software is Blender. Blender can probably do it because they have been receiving millions in donations from major game development companies in the recent years. Unless something similar happens in the field of photography, I don't think we'll be able to get away from proprietary software soon.
I find gimp's MDI workflow better than PSs single window UI.
I've used only Lightroom (as Adobe product), and it's hard to define what casual editing is, but the basic enhancement functionalities were easy to use, and especially, they were very effective (again, for a casual user).
It had, as far as I remember, very good automatic enhancement, that one could use as a base. The other products I tried weren't so effective. If, as I suppose, this type of functionality requires a significant investment to develop, then it's out of reach for non-very-well-funded open source development.
Dehazing was another typical example of LR functionality: it's stupid simple (a slider), and does effectively what's supposed to do for a casual user.
One tiny example: https://github.com/darktable-org/darktable/issues/7332
(Most) users are not going to adjust their core working styles - which have been consistent on the Mac platform for 35+ years - to use a piece of software that gives inferior results, just to save $10 / month - which also gives access to Photoshop, for which there is no true replacement in any case.
And as mentioned in the issue you linked it isn't a bug but a feature request to support macOS hotkey conventions. There is a workaround in the meantime documented and a suggestion on how to address the feature request (that requires refactoring of the codebase) on the non-dupe ticket.
Since this is libre software anyone can improve the code along those lines and send a merge request or even commission a developer to do that refactoring; the DarkTable maintainers _didn't_ refuse contributions nor marked it as wontfix however that doesn't mean that the maintainers have development-time to spare in that macOS-specific code.
On the other hand if not using macOS hotkey convention is an example of it being "unusable" then I guess it is really great for something most people don't pay a penny or contribute otherwise for.
One day I wanted to improve getting started documentation in open source f.lux alternative for linux, because it didn't work for me in Ubuntu without any visible error. I found the solution investigating terminal logs and did a 5 point write up "How to setup on Ubuntu".
Readme pull request got denied because "only one point applies to Ubuntu" (others were applicable to other distributions, too). Somebody even commented few months later that he found my pull request and it helped him make it work on his machine.
This mostly made me stop contributing to other projects.
Even the latest versions of GIMP and Krita are nowhere near capable of doing the things that I did in Photoshop 2.5 back in the early 1990s. I am not sure what the priorities are of the GIMP devs, but it seems like they aren’t at all serious about making a Photoshop alternative.
The list gets much, much longer when you compare GIMP to newer versions of Photoshop, like Photoshop 5 from 1998. Photoshop 5 completely blows GIMP out of the water in terms of both features and usability, it’s a complete joke.
I don’t use Photoshop any more, and I’ve exited the Adobe ecosystem, but once you’ve used tools like Photoshop, using GIMP feels like swapping your nice DSLR for an old point-and-shoot. Sure, you’re saving a lot of money, but you are constantly reminded that you developed a bunch of skills that you can’t use any more.