Looking for an open source equivalent to Diffzilla

[vanschoo at acm.org (Nancy Van Schooenderwoert)]

I'm mostly using the Kate editor, but I miss having a good visual diff
tool like "Diffzilla" that comes as part of SlickEdit. Here's a
description of its capabilities:

"DIFFzilla allows software developers to view changes between two files,
directories or directory trees - with feature-rich side-by-side editing
and color coding capabilities enabled for over 30 programming languages,
including Java, C/C++, C#, HTML, XML, Unicode and COBOL. DIFFzilla
fulfills a critical but often limited or missing function within the
software development lifecycle by allowing developers to view which
symbols and functions were changed or added in new versions, view what
changed on each line and merge three versions of a file back into one.
Unlike most differencing products, DIFFzilla allows developers to edit
and update files being compared in real time, thereby saving
considerable development time."

Can anyone recommend something that is similar?

- Nancy V.