"When you're editing text, you may find yourself with two or
three similar versions of a file. Often you are not sure which file
has what content, what was deleted in one, what was added in
another, and where exactly. You know what content your file should
contain, but you are not sure which version to start from. It's one
of those moments you wish your computer were smart enough to
understand your problem and fix it for you. Well, that's not going
to happen, but there is an open source application that you can run
to help. Meet Meld, a visual diff and merge tool.
"With Meld you can compare two or three files and edit them in
place (diffs update dynamically). You can compare two or three
directories and launch file comparisons. And lastly, you can browse
and view a working copy from a popular version control systems such
as CVS, Subversion, Bazaar, or Mercurial..."