Back when I hadn't had a Pentax camera yet, only a little Nikon 1 V1, I used Nikon ViewNX, which was packaged with the camera for free, to convert RAWs. I switched to DxO Optics when, I think it was version 9 in the base edition, was offered for free. I had tried RawTherapee and Darktable for a very short time, but - at the time and with my personal abilities and demands at the time - found them not to be very intuitive. I think I upgraded DxO Optics at least once to version 10 and/or 11, which was also offered for free at one time. I added the NIK Collection when it was offered by Google for free (the current version is sold by DxO now).
Those freebies above were what made me consider buying the current version of
DxO PhotoLab in the Elite edition (for the Dehaze filter "ClearView", but especially for the PRIME denoise algorithm, and the U-Point technology to make localized adjustments comes in handy as well), when it was sold at a great discount, and I added in ViewPoint as well to get easier perspective correction.
Depending on the pictures and my mood, I'll perhaps put them through one of the
NIK Collection plugins, say for converting to black and white, or adding a colour filter,...
I usually don't edit my own photos with it, but when I want to make a photo montage ("to photoshop something"), I'll put the input images into the free
GIMP. It took me a while to get used to the possibilities and how to work with them through the GUI, which can be very overwhelming at first if you have no idea what all those symbols mean, but now I think I can make most of what I want to do work, not very fast and not in the best way and not for perfect results, but with enough time I can get it good enough for my demands, mostly just by working with several layers, adding layer masks, editing those with a brush, and then resizing, moving and rotating the elements.
When I want to create a focus stack, I'll use the free and older
CombineZP. It offers several methods and I can just let it run all of them and choose the picture I like best out of all the results.
I think I once used
Hugin to stack some images of the night sky, I tried to stay close to a tutorial and that's what they used there. I think nowadays folks use
Sequater and/or
Deep Sky Stacker for this? At least one of the bunch should be free.
Microsoft ICE for panoramas (I think Hugin is an alternative for this as well?).
And for viewing, looking at basic EXIF parameters, comparing, cropping, resizing, saving, renaming, rotating, even clone/repair works well with it,... those basic operations, most of which (all?) can be done as batch operation on a whole folder of pictures as well, I use the
FastStone Image Viewer.
I don't have or use a program to organize my photos in a way that Lightroom offers it. I sort everything in folders, by year, and ideally add to the DATE when the photos were taken WHAT/WHERE/WHOM I photographed, and perhaps LENS(ES) I used, to be able to quickly find something I'm looking for. Speaking of which, I don't think I've taken the time this year to name the folders yet... which I wanted to do before I get my backups up to date... And I don't have an automated backup procedure in place, so I REALLY should be getting started with this sooner rather than later.