... and why?
I have a Linux workstation where I do most of my photo manipulation. I also use a PC.
I'm currently using Digikam, partly because it's free, partly because its editor has some features I like. I also use paint.net.
Start with Digikam:
The picture manager is pretty standard - you can arrange photos in albums, tag faces, rate, etc. I tend to be pretty simple in my wants - I put photos into albums based on dates and/or events. I don't do geo-tags and have very minimal face tags.
I use their local contrast and sharpen filters a lot, partly because my cameras tend to have somewhat soft focus. I also use their free transform quite a bit (I have a bit of a problem keeping my horizontals straight...)
Paint.net has a tool which allows you to rotate the picture over all three dimensions by moving a point on a spherical space. It's easier to do than it is to describe, and will let you fix some kinds of perspective and angle problems very easily. I use Digikam for everything else, but that tool is worth having for me.