In diff tool speak, a visual diff tool is a GUI application. Meld is such a tool: a tool for displaying differences between files (and directories) and also for merging the differences. Meld is programmed in Python.

Meld can compare two or three files or folders and provides a simple way to merge differences. With just a double click you can copy the differences between the instances.

If you are comparing two directories you can double click on a file to open it and it's corresponding version in the second directory and view their differences. In the directory view you can choose to hide what might be trivial differences, such as binaries and backup files.

Meld also works with several versioning systems, such as CVS, SVN and Mercurial.