File and directory comparison tool?

Meld

Meld is a tool that can compare and merge files and directories. It is a GUI analog to the standard diff and patch command line tools. (See man diff and man patch for more details on those)

Also, lots of source control systems (such as bzr or git ) have the ability to create diffs between versions.

Diff is your friend.

diff -ur path1 path2

This will compare all files that are common between path1 and path2.

If you change -ur to -urN then that will also show the contents of files that are only present in one of the paths.

'Beyond Compare' is available for Linux, too. Check their download URL.
Their german site is at http://www.beyondcompare.de/.