[jraph]

Meld here, for years. It is capable of editing in place and three way compare. It's a very good tool, and quite lightweight too.

I'd rather use KDE software though, since my desktop environment of choice is Plasma. I haven't found the edition-in-place feature in KDiff3. Is it there? Kate also being my code editor of choice, that would be amazing. If it's not there, how do you solve merge conflicts with KDiff3 if you don't have editing in place?

[Nursie]

Meld is a great, free tool available on pretty much all platforms. Been using it for a long old time now and can't recommend it enough.

2-way, 3-way and folder diff, in-place editing, it has all I need.

[dikei]

Kdiff3 can absolutely do edit in place: just type directly in the merge output window and save the result as usual.