Winmerge for OSX
Slightly spurious title as there is absolutely no need for a winmerge for OSX. Included with the Developer Tools for OSX is
filemerge, which is an excellent diff tool. There is also a tool to call it from a terminal called
opendiff so you can do
opendiff dir1 dir2 opendiff file1 file2
You can also find filemerge using spotlight.