GNU Emacs has the very good "ediff" mode. I use it and press a or b frequently.

And power users get more fancy, e.g. : https://emacs.stackexchange.com/questions/16469/how-to-merge-git-conflicts-in-emacs

And it has lots of powerful features. Expanded help menu:

Wow, I haven't looked at the menu in so long it has features I forgot it had.

Emacs is available for every *nix platform. And its as open source as it gets.

I use it so often that typing M-x ediff took too long, so I bound it to C-c C-e.

GNU Emacs has the very good "ediff" mode. I use it and press a or b frequently.

And power users get even more fancy, e.g. : https://emacs.stackexchange.com/questions/16469/how-to-merge-git-conflicts-in-emacs

And it has lots of powerful features. Expanded help menu:

I highly recommend committing the capabilities shown in the menu to memory, so you use them when they'd be useful. (Wow, I haven't looked at the menu in so long it has features I forgot it had.)

Emacs is available for every *nix platform. And its as open source as it gets.

I use ediff so often that typing M-x ediff took too long, so I bound it to C-c C-e.