NYCJUG/WinDiff
Here's a screenshot from the software package WinDiff. It's an example of useful, innovative software interface design.
This shows the differences between two text files. The frame on the left gives a view of the whole of both files; lines present in the left-hand file but not in the other are indicated by red; lines present in the right-hand file but not the other are indicated by yellow. This part of the display is discussed in more detail below.
The large-scale view on the left is complemented by the detailed view on the right in which the deletions and insertions are shown line-by-line.
Looking closely at the left-hand frame, we see the (partial) file names at the top with some colored bars below. Looking at the first colored bar on the far left, we see a blue bar indicating the length of the left-hand file; the blue bar on the far right shows that the corresponding file is longer.
The white bars with lines between the left and right show us which parts of the two files are the same. Lines of text present in one file but not the other are shown in red for the left-hand file and yellow for the file which is named by the left argument to this function.