Good diff/merge utility for non-Windows platforms?

In My Humble Opinion
1

I’m using Winmerge, and it’s a great program, but it only runs on Windows. What’s a good (and preferably free) tool for other platforms?

2

Uh… you know where the term “diff” comes from, right?

diff

Also… patch

3

I like DiffMerge, and KDiff3 (both free.)

Also take a look at this link: http://en.wikipedia.org/wiki/Comparison_of_file_comparison_tools